Backseamed casing and packaged product incorporating same

ABSTRACT

A heat-shrinkable backseamed casing film comprises a first layer, a second layer, and a third layer, with the first and third layers being outer layers and the second layer being between the first layer and the third layer. The first outer layer serves as an inside casing layer, and comprises polyolefin; the second layer comprises polyester and/or polyamide; the third layer serves as an outside casing layer and comprises polyolefin, polystyrene, and/or polyamide. The second layer has a thickness of at least about 5% of a total thickness of the heat-shrinkable casing film. Alternatively, the first layer comprises polyolefin and has a surface energy level of less than about 34 dynes/cm; the second layer comprises a polyamide having a melting point of at least 300° F.; and the third layer comprises polyolefin, polystyrene and/or polyamide. A package comprises a cooked meat product within the backseamed casing. The second layer of the casing film prevents or reduces necking down on the forming shoe during backseaming. The backseamed casing is especially useful for cook-in applications.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation-in-part of copending U.S. Ser.No. 08/951,245, filed in the U.S. Patent and Trademark Office on Sep.25, 1992, in the name of R. K. Ramesh.

FIELD OF THE INVENTION

[0002] The present invention relates generally to multilayer films, andparticularly to multilayer films suitable for use in backseamed casingsfor packaging meat products. The present invention is particularlyrelated to backseamed casings suitable for packaging protein-containingfood products in which the film adheres to the food product, andespecially to those having a relatively high protein content, alsocalled ‘low-fat’ food products, such as poultry, ham, roast beef, etc.The present invention is also directed to packages.

BACKGROUND OF THE INVENTION

[0003] Processed meat products, such as poultry and ham, are oftenpackaged in a flexible, thermoplastic, heat-shrinkable film tubingcommonly referred to as a casing. Although some casings have a lay-flatwidth of 6-20 inches, some products, such as ham, etc., are quite oftenpackaged in a casing of smaller lay-flat width, e.g., a width of fromabout 3 to 6 inches. Such casings often may need to have aprecisely-controlled width, because the packages are stated as having agiven weight, which is uniform among packages, and the packages alsohave product sliced at uniform intervals, with each package containingthe same number of slices. Thus, variations in casing width can resultin both an undesirable degree of variation in overall package weight, aswell as an undesirable degree of variation in slice weights.

[0004] Thus, there is a need for a casing having a small and uniformdiameter. However, it is relatively difficult to make a narrow width,heat-shrinkable seamless casing having a precisely controlled width,using a commercially feasible process. Consequently, there is a need forsome other process for making a narrow-width, precisely-width-controlledcasing.

[0005] Some backseamed casings are known to be casings of small anduniform diameter. Small-diameter backseamed casings are known which havea precisely controlled casing width, i.e., a lay-flat width independentof film extrusion variations. In the production of backseamed casings(e.g., using a backseaming machine such as a Nishibe HSP-250-SAbackseaming machine obtained from Nishibe Kikai Co. Ltd. of Nagoya,Japan), a flat sheet of film is folded longitudinally by passage over a“forming shoe”. A forming shoe is a part of the backseaming machinewhich the film is passed under and around, i.e., so that the initiallyflat film is reconfigured as a tube, having a longitudinal overlap andseal therealong (lap-sealed backseamed casing), or with filmlongitudinal edges abutted against one another (butt-sealed backseamedcasing), with the width of the tube being determined by thecircumference of the forming shoe. A longitudinal lap or butt seal isthen applied while the film is between the forming shoe and a sealingdevice, resulting in a lap-sealed backseamed casing, or a butt-sealedbackseamed casing. Butt-seal casings utilize a butt-seal tape sealed tothe inside or the outside surface of the casing film, along both sidesof the abutting longitudinal seam of the casing film. In either event,the resulting tubing, termed a “backseamed casing,” is sealed or clippedat its ends after being filled with a meat product. For some uses, themeat product is thereafter cooked while in the backseamed casing.

[0006] It would be desirable to provide a highly uniform, small diameterbackseamed casing suitable for cook-in end use, the casing being madefrom a film which adheres to high-protein meat products, such as certaingrades of ham and turkey. Of course, it would also be desirable toprovide the backseamed casing with a backseam seal which survives thecook-in process.

[0007] It is known that a polar surface is needed for adhesion of a filmto a meat product. Adhesion of the film to the meat is frequently neededin order to prevent “purge”, i.e., cook-out, which can occur during thecooking of the meat packaged in the film if the film does adhere to themeat during cook-in. A polar film surface can be provided by using: (a)polar resin in the film layer in contact with the meat, and/or (b)surface modification, such as corona treatment, of the film surface incontact with the meat. Typically, polar polymers used for meat adhesioninclude: ethylene/unsaturated acid copolymer, anhydride-containingpolyolefin, and polyamide.

[0008] Film-to-meat adhesion is known to be enhanced by corona treatmentof the surface of the film to which the meat is to be adhered. However,corona treatment alters the film surface in a manner which can, onoccasion, result in an inferior seal, i.e., a seal more likely to leakthan if the film surface is not corona treated. This “leaky sealproblem” can be avoided by “buffing off” the corona treatment in thearea of the seal, so that the advantageous effects of the coronatreatment, i.e., greater meat adhesion, can be retained on the majorityof the meat-contact surface of the film, while at the same timeavoiding, in the area of the seal, the seal-quality problem caused bythe corona treatment. However, the buffing step is undesirable, as it isan additional processing step which renders the casing manufacture morecomplex and costly. Furthermore, the buffing step is frequentlyinconsistent.

[0009] Since the backseaming process is generally carried out after thecorona treatment, shrinkage of the film against the forming shoe (duringbackseaming), coupled with forwarding the film over the forming shoeafter shrinkage, results in the rubbing of the film against the formingshoe edges. This rubbing reduces or destroys corona treatment, at leastin the area in which the film rubs against the forming shoe. As aresult, backseamed casings containing corona treated films can exhibitpurge at the locations at which the film rubs against the forming shoe.Furthermore, corona treatment can be inconsistent, at least with respectto prevention of purge for products having an intermediate proteincontent. It would be desirable that the casing film has a consistent andadequate level of protein/meat adhesion. As a result, it would bedesirable to provide a corona-treatment-free backseamed casing whichprevents purge from products relatively high in protein, where theadhesion of the casing film to the meat product is uniform over thefilm.

[0010] Thus, it would be desirable to provide a backseamed casing ofsmall and uniform diameter which is heat-shrinkable and suitable forcook-in end use, exhibits good purge-resistance and good seal strength,can be economically manufactured, does not produce significant meatpull-off upon being stripped from a cooked meat product, and whichprovides a good oxygen barrier, in order to provide good shelf life tothe cooked meat product.

[0011] Heat-shrinkable films having an outer layer capable of providingmeat adhesion, which are otherwise suitable for use as backseamedcasings, have been found to have the undesirable characteristic ofnecking down on the forming shoe during the backseaming process. Thenecking down on the forming shoe is believed to be due to shrinkage ofthe film during the heat sealing step of the backseaming operation. Thatis, the heat sealing step can cause substantial film shrinkage in anarea extending outward from the seal, causing the edges of the casing toneck down on the forming shoe. The result of necking down is a casinghaving “ruffled edges”, i.e., visible nonuniformities in the casing. Inan extreme case, necking down results in the rupture of the film, as theshrinking of the film against the forming shoe places so much force onthe film that the film ruptures. Thus, it would be desirable to providea casing film which does not shrink down (i.e., “neck down”) on theforming shoe during the backseaming operation.

SUMMARY OF THE INVENTION

[0012] It has been discovered that the presence of an inner layercomprising a polyamide, preferably a high modulus polyamide, provides,if the polyamide layer makes up at least 5 percent of the total filmthickness, a film which does not neck down on the forming shoe duringthe backseaming operation. Although the reasons why the inner polyamidelayer prevent necking down on the forming shoe are not currently knownwith certainty, it is believed that various factors, including heattransfer, shrink characteristics, etc. bring about the discoveredadvantage of not necking down on the forming shoe. Furthermore, theinner polyamide layer also helps to provide a better quality casing filmby making the casing film easier to orient, facilitating fasterbackseaming speeds, and also imparting enhanced seal strength,toughness, pin-hole resistance and elastic recovery to the casing film.

[0013] It has also been discovered that in the case ofanhydride-containing polyolefin, if the anhydride functionality is ofthe order of 1 weight percent or less, the polymer often does notprovide adequate meat adhesion to intermediate-protein-containing meatproducts, or low-protein-containing meat products. On the other hand,polymers such as polyamide can, in some instances, provide too muchmeat-adhesion and tend to pull meat off during unpackaging of the meat,thereby destroying the smooth surface desired upon separating the casingfilm from the cooked meat product, and also contributing to yield loss.Polyamides are also relatively expensive polymers. Thus, it would bedesirable to provide a casing having a film providing adequate meatadhesion to prevent purge, while being able to strip the film from themeat without meat pull-off due to too much adhesion of the film to thecooked meat product. However, it has been found that adequate meatadhesion can be obtained using an anhydride-containing polyolefin havingan anhydride functionality of at least 1 percent.

[0014] As a first aspect, the present invention is directed to abackseamed casing comprising a heat-shrinkable casing film. The heatshrinkable film comprises a first layer, a second layer, and a thirdlayer, with the first and third layers being outer layers and the secondlayer being between the first layer and the third layer. The first outerlayer serves as an inside casing layer, and comprises a firstpolyolefin. The first polyolefin comprises at least one member selectedfrom the group consisting of: (i) ethylene/unsaturated acid copolymer,propylene/unsaturated acid copolymer, and butene/unsaturated acidcopolymer, wherein the unsaturated acid is present in an amount of atleast 4 weight percent, based on the weight of the copolymer; and (ii)anhydride-containing polyolefin comprising an anhydride-functionality,wherein the anhydride functionality is present in an amount of at least1 weight percent, based on the weight of the anhydride-containingpolyolefin. The second layer comprises at least one member selected fromthe group consisting of polyester, and first polyamide. The third layerserves as an outside casing layer, and comprises at least one memberselected from the group consisting of second polyolefin, polystyrene,and second polyamide. The second layer has a thickness of at least about5% of a total thickness of the heat-shrinkable casing film.

[0015] In the first layer, the first polyolefin preferably comprises anethylene/unsaturated acid copolymer having an unsaturated acid merpresent in an amount of at least 6 percent, based on the weight of theethylene/unsaturated acid copolymer; more preferably, the unsaturatedacid is present in an amount of at least 9 weight percent, based on theweight of the ethylene/unsaturated acid copolymer.

[0016] The first layer preferably further comprises a third polyolefincomprising at least one member selected from the group consisting ofpolyethylene homopolymer, polyethylene copolymer, polypropylenehomopolymer, polypropylene copolymer, polybutene homopolymer, andpolybutene copolymer. More preferably, the third polyolefin comprises atleast one member selected from the group consisting ofethylene/alpha-olefin copolymer, propylene/alpha-olefin copolymer,butene/alpha-olefin copolymer, ethylene/unsaturated acid copolymer, andethylene/unsaturated ester copolymer. Still more preferably, the thirdpolyolefin comprises at least one member selected from the groupconsisting of linear low density polyethylene (LLDPE),propylene/ethylene copolymer, and propylene/butene copolymer. Yet stillmore preferably, the third polyolefin comprises LLDPE.

[0017] The second layer preferably comprises the first polyamide. Morepreferably, the first polyamide comprises at least one member selectedfrom the group consisting of polyamide 6, polyamide 66, polyamide 9,polyamide 10, polyamide 11, polyamide 12, polyamide 69, polyamide 610,polyamide 612, polyamide 6I, polyamide 6T, and copolymers thereof. Stillmore preferably, the first polyamide comprises at least one memberselected from the group consisting of polyamide 6, polyamide 66 andcopolyamide 6/66.

[0018] The third layer preferably comprises the second polyolefin.Preferably, the second polyolefin has a vicat softening point of atleast 80° C.; more preferably, at least 90° C.; and still morepreferably, at least 100° C. The softening point of the secondpolyolefin has to be high enough to undergo cook-in without causing theseals to fail (if the polyolefin is used in a seal layer). In analternative preferred embodiment, the third layer comprises the secondpolyamide, with or without the second polyolefin, more preferably, as analternative to the second polyolefin.

[0019] Preferably, the casing film further comprises a fourth layer, thefourth layer being an inner layer serving as an O₂-barrier layer, thefourth layer comprising at least one member selected from the groupconsisting of ethylene/vinyl alcohol copolymer, polyvinylidene chloridecopolymer, polyethylene carbonate copolymer and polyamide. Preferably,the second layer and the fourth layer are directly adhered.

[0020] Preferably, the casing film further comprises a fifth layer and asixth layer, wherein: (a) the fifth layer is between the first layer andthe second layer, and the sixth layer is between the second layer andthe third layer; (b) the fifth layer comprises at least one memberselected from the group consisting of fourth polyolefin, polystyrene andpolyurethane; and (c) the sixth layer comprises at least one memberselected from the group consisting of fifth polyolefin, polystyrene andpolyurethane. Preferably, the fifth layer is a tie layer and comprisesat least one member selected from the group consisting of modifiedethylene/alpha-olefin copolymer, modified ethylene/unsaturated estercopolymer, and modified ethylene/unsaturated acid copolymer. Preferably,the sixth layer is a tie layer and comprises at least one memberselected from the group consisting of modified ethylene/alpha-olefincopolymer, modified ethylene/unsaturated ester copolymer, and modifiedethylene/unsaturated acid copolymer.

[0021] Preferably, the casing film further comprises: (a) a seventhlayer, the seventh layer being between the first layer and the secondlayer, the seventh layer comprising a sixth polyolefin; and (b) aneighth layer, the eighth layer being between the second layer and thethird layer, the eighth layer comprising a seventh polyolefin.

[0022] Preferably, a ratio of: (a) a sum of the thickness of the firstlayer and the fifth layer; to (b) a sum of the thickness of the thirdlayer and the sixth layer is from about 0.7:1 to 1.3:1. Preferably thesecond layer has a thickness of from about 5 to 20 percent, based on atotal thickness of the multilayer film; and preferably, the fourth layerhas a thickness of less than about 15%, based on a total thickness ofthe multilayer film. Preferably, the heat-shrinkable casing film hasbiaxial orientation. Preferably, the casing film has a free shrink, at185° F., of at least 10% in at least one direction. Preferably, at leasta portion of the casing film comprises a crosslinked polymer network.

[0023] The backseamed casing according to the present invention can beeither a lap-sealed backseamed casing or a butt-sealed backseamedcasing. A butt-sealed casing comprises both a casing film and abutt-seal tape film. Preferably, the butt-seal tape film comprises atleast one member selected from the group consisting of polyolefin,polyamide or polystyrene, and preferably the butt-seal tape film isheat-shrinkable.

[0024] As a second aspect, the present invention is directed to apackage comprising a cooked meat product within a backseamed casing. Thebackseamed casing is according to the first or third aspects of thepresent invention described herein, and the cooked meat product isadhered to a meat-contact surface of the casing film.

[0025] Preferably, the meat product comprises at least one memberselected from the group consisting of poultry, ham, beef, lamb, fish,liver sausage, bologna, mortadella, braunschweiger, goat, and horse;more preferably, poultry, ham, beef, lamb, fish, liver sausage, bologna,and mortadella. Preferably, the meat-contact surface of the first layeris corona treated, and the meat product comprises at least one memberselected from the group consisting of liver sausage, bologna andmortadella. Preferably, the outside surface of the casing film is alsocorona treated. Preferably, the meat comprises from 0-30% fat, morepreferably from 1-15% fat, still more preferably from 2-10% fat, and yetstill more preferably from 3-7% fat. Preferred backseamed casings foruse in the package include the preferred backseamed casings inaccordance with the present invention.

[0026] If a non-corona treated backseamed casing (or equivalent thereofaccording to the first aspect of the present aspect is used, the cookedmeat product preferably comprises at least one member selected from thegroup consisting of turkey, ham, beef, and fish, wherein the meatproduct comprises fat in an amount of from about 2 to 10 weight percent,preferably 3 to 8 percent, and more preferably from about 4 to 6percent. If a corona treated backseamed casing (or equivalent thereof)according to the first aspect of the present aspect is used, the cookedmeat product preferably comprises at least one member selected from thegroup consisting of ham, beef, liver sausage, bologna, mortadella,horse, and goat; more preferably, the meat product comprises at leastone member selected from the group consisting of ham, liver sausage,bologna, and mortadella; preferably, the cooked meat product comprisesfat in an amount of from about 3 to 40 weight percent, preferably 5 to30 percent, and more preferably from about 10 to 15 percent.

[0027] If a non-corona treated backseamed casing (or equivalent thereof)according to the third aspect of the present aspect is used, the cookedmeat product preferably comprises at least one member selected from thegroup consisting of turkey and fish, wherein the meat product comprisesfat in an amount of from about 1 to 10 weight percent, preferably 2 to 6percent, and more preferably from about 3 to 5 percent.

[0028] As a third aspect, the present invention is directed to abackseamed casing comprising a heat-shrinkable casing film comprising:(A) a first outer layer serving as an inside casing layer, the firstouter layer comprising a first polyolefin, the first outer layer havinga surface energy level of less than about 34 dynes/cm; (B) a secondlayer comprising a first polyamide having a melting point of at least300° F.; (C) a third layer serving as an outside casing layer, the thirdouter layer comprising at least one member selected from the groupconsisting of a second polyolefin, polystyrene and second polyamide. Thesecond layer is between the first layer and the third layer, and thesecond layer has a thickness of at least about 5% of a total thicknessof the heat-shrinkable casing film.

[0029] In a lap-sealed backseamed casing according to this third aspectof the present invention, preferably the first polyolefin has a vicatsoftening point of at least 70° C., more preferably at least 80° C., inorder to provide a desired level of seal strength. However, in abutt-sealed backseamed casing according to this third aspect of thepresent invention, the vicat softening point of the first polyolefin maybe less critical. More preferably, the first polyolefin is a relativelynon-polar polymer, preferably having a surface energy level of less than32 dynes/cm.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 illustrates a cross-sectional view of a lap-seal backseamedcasing in accord with the present invention.

[0031]FIG. 2 illustrates an enlarged cross-sectional view of a firstpreferred casing film suitable for use in the lap-seal backseamed casingillustrated in FIG. 1.

[0032]FIG. 3 illustrates an enlarged cross-sectional view of a secondpreferred casing film suitable for use in the lap-seal backseamed casingillustrated in FIG. 1.

[0033]FIG. 4 illustrates an enlarged cross-sectional view of a thirdpreferred casing film suitable for use in the lap-seal backseamed casingillustrated in FIG. 1.

[0034]FIG. 5 illustrates a cross-sectional view of a butt-sealbackseamed casing in accord with the present invention.

[0035]FIG. 6 illustrates an enlarged cross-sectional view of a firstpreferred casing film suitable for use in the butt-seal backseamedcasing illustrated in FIG. 5.

[0036]FIG. 7 illustrates an enlarged cross-sectional view of a firstpreferred butt-seal tape film suitable for use in the butt-sealbackseamed casing illustrated in FIG. 5.

[0037]FIG. 8 illustrates a schematic view of a process for making apreferred heat-shrinkable casing film and/or butt-seal tape film, foruse in a backseamed casing in accord with the present invention.

[0038]FIG. 9 illustrates a perspective view of a first package accordingto the present invention.

[0039]FIG. 10 illustrates a perspective view of a second packageaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0040] As used herein, the term “package” and the phrase “packagedproduct” refer to an article in which a product (preferably a foodproduct, more preferably a meat-containing food product) is encased in apackaging film.

[0041] As used herein, the phrase “lay-flat film” refers to a film thathas been extruded as a wide, thin-walled, circular tube, usually blown,cooled, then gathered by converging sets of rollers and wound up inflattened form. The phrase “lay-flat width”, refers to half of thecircumference of the inflated film tube.

[0042] As used herein, the phrase “backseamed casing” refers to anycasing (a tubular film) having a longitudinal seal. For example, alap-seal backseamed casing can be formed: by folding a film strip over aforming shoe of a horizontal sealing machine, and applying alongitudinal seal thereto where the film overlaps, e.g. using a NishibeModel HSP-250-SA sealing machine; or a Totani Model FD-350C sealingmachine obtained from Totani Giken Kogyo Co., Ltd., of Kyoto, Japan; or,by folding a film strip over a forming shoe of a vertical form fill andseal machine, and applying a longitudinal seal thereto where the filmoverlaps, e.g., using an ONPACK-2002 (TM) sealing machine, obtained fromOrihiro Company, Ltd., of Tomioka City, Japan. A lap-sealed casing couldalso use a tape-film in between the areas where the film overlaps, tofacilitate sealing. A butt-seal backseamed casing can be formed: byfolding a film strip over a forming shoe of a horizontal sealingmachine, with opposing longitudinal edges abutting one another, i.e., innon-overlapping relation to one another; and thereafter, by applying abutt-seal tape film over the abutting edges, followed by sealing thebutt-seal tape film across and along the abutting edges, so that asealed tube is formed.

[0043] For the backseamed casings according to the present invention,the composition in the second layer can be present either in one or morelayers of the casing film. If the composition is present in more thanone layer, the layers are preferably so positioned as to providereasonable symmetry to the film, thus providing a relatively flat,curl-free film.

[0044] Preferably, the backseamed casing according to the presentinvention has a lay-flat width of at less than about 10 inches; morepreferably, from about 1 to 10 inches, still more preferably, from about2 to 8 inches; yet still more preferably, from about 3 to 7 inches, andyet still even more preferably, from about 4 to 6 inches. It is believedthat for any given film to be backseamed, the problem of necking down onthe forming shoe becomes worse as the lay-flat width of the casing isreduced.

[0045] Heat-shrinkable multilayer films of the invention preferably havea substantially symmetrical cross-section, with respect to both layerthickness and layer chemical composition, in order to provide the filmwith relatively low curl. For example, for a 3-layer casing filmaccording to the backseamed casing of the present invention, the ratioof a/b is preferably from about 0.7-1.3, more preferably from about0.8-1.2, and even more preferably from about 0.9-1.1; wherein, ‘a’ isthe thickness of the first outer layer and ‘b’ is the thickness of thesecond outer layer. For a preferred six-layer casing film in accordancewith the backseamed casing of the present invention, the ratio of thesums of the thickness of the first layer plus the fifth layer to the sumof the second layer plus the sixth layer is preferably from about0.7-1.3; more preferably from about 0.8 to 1.2; and still morepreferably, from about 0.9 to 1.1.

[0046] The heat-shrinkable casing film according to the presentinvention preferably has a free shrink of from about 5-70 percent in oneor both directions (i.e., longitudinal direction “L”, also referred toas “machine direction”, and transverse direction, “T”) at 185° F.,determined according to ASTM D 2732; more preferably, from about 10-50percent at 185° F.; still more preferably, from about 15-35 percent at185° F. Preferably, the casing film is biaxially oriented, andpreferably the film has a free shrink, at 185° F., of at least 10percent in each direction (L and T); more preferably, at least 15percent in each direction. Preferably, the casing film has a total freeshrink of from about 30 to 50 percent (L+T) at 185° F. For a butt sealbackseamed casing, the butt seal tape film can be either aheat-shrinkable film or a non-heat-shrinkable film.

[0047] As used herein, the term “sealed” refers to any and all means ofclosing a package, such as heat sealing via hot air and/or heated bar,ultrasonic, radio frequency sealing, and even the use of clips on, forexample, a shirred casing, etc. As used herein, the phrase “heat seal”refers to a seal formed by contacting the film with a hot element, e.g.,using a hot bar, hot wire, hot air, etc.

[0048] Preferably, the seal in the backseamed casing according to thepresent invention has a seal strength of at least 3 pounds per inch (asmeasured on an Instron, per ASTM F88); more preferably, from about 5 to100 lb/in; still more preferably, from about 7 to 50 lb/in; yet stillmore preferably, from about 10 to 30 lb/in; and yet still morepreferably, from about 15 to 20 lb/in.

[0049] As used herein, the phrase “butt seal” refers to a seal formed bybutting opposing film edges together and thereafter sealing regions inthe vicinity of the abutted edges to a butt seal tape, as shown in FIG.5.

[0050] As used herein, the phrase “lap seal” refers to a seal formed bylapping a film over itself to form a package by sealing an insidesurface of the film to an outside surface of the film, as shown in FIG.4.

[0051] As used herein, the phrase “meat-contact layer”, refers to alayer of a multilayer film which is in direct contact with themeat-containing product packaged in the film. The meat-contact layer isan outer layer, in order to be in direct contact with the meat product.The meat-contact layer is an inside layer in the sense that in thepackaged meat product, the meat-contact layer is the innermost filmlayer in direct contact with the food.

[0052] As used herein, the phrase “meat-contact surface” refers to asurface of a meat-contact layer which is in direct contact with the meatin the package.

[0053] As used herein, the phrase “meat-adhesion”, and “adhered”, referto maintaining direct contact between the meat surface and themeat-contact surface of the film, so that there is an absence of fat ora substantial amount of free moisture, e.g., juices emitted outside ofthe meat product, commonly referred to as “purge”. In general, there isan absence of a substantial amount of free moisture if the level of freemoisture is from about 0 to 2%, based on the weight of the meat productbefore cooking. Preferably the amount of free moisture is from about 0to 1%, more preferably, 0 to 0.5%, and still preferably from 0 to 0.1percent based on the weight of the meat product before cooking.

[0054] As used herein, the phrase “cook-in” refers to the process ofcooking a product packaged in a material capable of withstandingexposure to long and slow cooking conditions while containing the foodproduct, for example cooking at 57° C. to 121° C. (i.e., 135° F.-250°F.) for 2-12 hours, preferably 57° C. to 95° C. (i.e., 135° F.-203° F.)for 2-12 hours. Cook-in packaged foods are essentially pre-packaged,pre-cooked foods which may be directly transferred to the consumer inthis form. These types of foods may be consumed with or without warming.Cook-in packaging materials maintain seal integrity, and in the case ofmultilayer films are delamination resistant. Cook-in films may also beheat-shrinkable under cook-in conditions so as to form a tightly fittingpackage. Cook-in films preferably have a tendency for adhesion to thefood product, thereby preventing “cook-out”, i.e., “purge”, which is thecollection of juices between the outer surface of the food product andthe meat-contact surface of the film, i.e., the surface in directcontact with the meat. Additional optional characteristics of films foruse in cook-in applications include delamination-resistance, low O₂permeability, heat-shrinkability representing about 20-50% biaxialshrinkage at about 85° C. (185° F.), and optical clarity.

[0055] As used herein, “EVOH” refers to ethylene vinyl alcoholcopolymer. EVOH includes saponified or hydrolyzed ethylene vinyl acetatecopolymers, and refers to a vinyl alcohol copolymer having an ethylenecomonomer, and prepared by, for example, hydrolysis of vinyl acetatecopolymers, or by chemical reactions with polyvinyl alcohol. The degreeof hydrolysis is preferably at least 50% and more preferably at least85%.

[0056] As used herein, the term “barrier”, and the phrase “barrierlayer”, as applied to films and/or film layers, is used with referenceto the ability of a film or film layer to serve as a barrier to O₂.

[0057] As used herein, the term “lamination”, and the phrase “laminatedfilm”, refer to the process, and resulting product, made by bondingtogether two or more layers of film or other materials. Lamination canbe accomplished by joining layers with adhesives, joining with heat andpressure, corona treatment, and even spread coating and extrusioncoating. The term laminate is also inclusive of coextruded multilayerfilms comprising one or more tie layers.

[0058] As used herein, the term “oriented” refers to apolymer-containing material which has been stretched at an elevatedtemperature (the orientation temperature), followed by being “set” inthe stretched configuration by cooling the material while substantiallyretaining the stretched dimensions. Upon subsequently heatingunrestrained, unannealed, oriented polymer-containing material to itsorientation temperature, heat shrinkage is produced almost to theoriginal unstretched, i.e., pre-oriented dimensions. More particularly,the term “oriented”, as used herein, refers to oriented films, whereinthe orientation can be produced in one or more of a variety of manners.

[0059] As used herein, the phrase “orientation ratio” refers to themultiplication product of the extent to which the plastic film materialis expanded in several directions, usually two directions perpendicularto one another. Expansion in the machine direction is herein referred toas “drawing”, whereas expansion in the transverse direction is hereinreferred to as “stretching”. The degree of orientation is also referredto as the orientation ratio, or sometimes as the “racking ratio”.

[0060] As used herein, the term “monomer” refers to a relatively simplecompound, usually containing carbon and of low molecular weight, whichcan react to form a polymer by combining with itself or with othersimilar molecules or compounds.

[0061] As used herein, the term “comonomer” refers to a monomer which iscopolymerized with at least one different monomer in a copolymerizationreaction, the result of which is a copolymer.

[0062] As used herein, the term “polymer” refers to the product of apolymerization reaction, and is inclusive of homopolymers, copolymers,terpolymers, etc. In general, the layers of a film can consistessentially of a single polymer, or can have still additional polymersblended therewith.

[0063] As used herein, the term “homopolymer” is used with reference toa polymer resulting from the polymerization of a single monomer, i.e., apolymer consisting essentially of a single type of repeating unit.

[0064] As used herein, the term “copolymer” refers to polymers formed bythe polymerization reaction of at least two different monomers. Forexample, the term “copolymer” includes the copolymerization reactionproduct of ethylene and an alpha-olefin, such as 1-hexene. However, theterm “copolymer” is also inclusive of, for example, the copolymerizationof a mixture of ethylene, propylene, 1-hexene, and 1-octene.

[0065] As used herein, the term “polymerization” is inclusive ofhomopolymerizations, copolymerizations, terpolymerizations, etc., andincludes all types of copolymerizations such as random, graft, block,etc. In general, the polymers, in the films used in accordance with thepresent invention, can be prepared in accordance with any suitablepolymerization process, including slurry polymerization, gas phasepolymerization, and high pressure polymerization processes.

[0066] As used herein, the term “copolymerization” refers to thesimultaneous polymerization of two or more monomers.

[0067] As used herein, a copolymer identified in terms of a plurality ofmonomers, e.g., “propylene/ethylene copolymer”, refers to a copolymer inwhich either monomer copolymerizes in a higher weight or molar percent.However, the first listed monomer preferably is polymerized in a higherweight percent than the second listed monomer, and, for copolymers whichare terpolymers, quadripolymers, etc., preferably, the first monomercopolymerizes in a higher weight percent than the second monomer, andthe second monomer copolymerizes in a higher weight percent than thethird monomer, etc.

[0068] As used herein, terminology employing a “/” with respect to thechemical identity of a copolymer (e.g., “an ethylene/alpha-olefincopolymer”), identifies the comonomers which are copolymerized toproduce the copolymer. Such phrases as “ethylene alpha-olefin copolymer”is the respective equivalent of “ethylene/alpha-olefin copolymer.”

[0069] As used herein, the phrase “heterogeneous polymer” refers topolymerization reaction products of relatively wide variation inmolecular weight and relatively wide variation in compositiondistribution, i.e., polymers made, for example, using conventionalZiegler-Natta catalysts. Heterogeneous polymers are useful in variouslayers of the film used in the present invention. Such polymerstypically contain a relatively wide variety of chain lengths andcomonomer percentages.

[0070] As used herein, the phrase “heterogeneous catalyst” refers to acatalyst suitable for use in the polymerization of heterogeneouspolymers, as defined above. Heterogeneous catalysts are comprised ofseveral kinds of active sites which differ in Lewis acidity and stericenvironment. Ziegler-Natta catalysts are heterogeneous catalysts.Examples of Ziegler-Natta heterogeneous systems include metal halidesactivated by an organometallic co-catalyst, such as titanium chloride,optionally containing magnesium chloride, complexed to trialkyl aluminumand may be found in patents such as U.S. Pat. No. 4,302,565, to GOEKE,et. al., and U.S. Pat. No. 4,302,566, to KAROL, et. al., both of whichare hereby incorporated, in their entireties, by reference thereto.

[0071] As used herein, the phrase homogeneous polymer refers topolymerization reaction products of relatively narrow molecular weightdistribution and relatively narrow composition distribution. Homogeneouspolymers are useful in various layers of the multilayer film used in thepresent invention. Homogeneous polymers exhibit a relatively evensequencing of comonomers within a chain, the mirroring of sequencedistribution in all chains, and the similarity of length of all chains,and are typically prepared using metallocene, or other single-site typecatalysis.

[0072] More particularly, homogeneous ethylene/alpha-olefin copolymersmay be characterized by one or more methods known to those of skill inthe art, such as molecular weight distribution (M_(u)/M_(n)),composition distribution breadth index (CDBI), and narrow melting pointrange and single melt point behavior. The molecular weight distribution(M_(u)/M_(n)), also known as polydispersity, may be determined by gelpermeation chromatography. The homogeneous ethylene/alpha-olefincopolymers useful in this invention will have a (M_(u)/M_(n)) of lessthan 2.7. Preferably, the (M_(u)/M_(n)) will have a range of about 1.9to 2.5. More preferably, the (M_(u)/M_(n)) will have a range of about1.9 to 2.3. The composition distribution breadth index (CDBI) of suchhomogeneous ethylene/alpha-olefin copolymers will generally be greaterthan about 70 percent. The CDBI is defined as the weight percent of thecopolymer molecules having a comonomer content within 50 percent (i.e.,plus or minus 50%) of the median total molar comonomer content. The CDBIof linear polyethylene, which does not contain a comonomer, is definedto be 100%. The Composition Distribution Breadth Index (CDBI) isdetermined via the technique of Temperature Rising Elution Fractionation(TREF). CDBI determination clearly distinguishes the homogeneouscopolymers used in the present invention (narrow compositiondistribution as assessed by CDBI values generally above 70%) fromheterogeneous polymers such as VLDPEs available commercially whichgenerally have a broad composition distribution as assessed by CDBIvalues generally less than 55%. The CDBI of a copolymer is readilycalculated from data obtained from techniques known in the art, such as,for example, temperature rising elution fractionation as described, forexample, in Wild et. al., J. Poly. Sci. Poly. Phys. Ed., Vol. 20, p.441(1982). Preferably, the homogeneous ethylene/alpha-olefin copolymershave a CDBI greater than about 70%, i.e., a CDBI of from about 70% to99%. In general, the homogeneous ethylene/alpha-olefin copolymers in themultilayer films of the present invention also exhibit a relativelynarrow melting point range, in comparison with “heterogeneouscopolymers”, i.e., polymers having a CDBI of less than 55%. Preferably,the homogeneous ethylene/alpha-olefin copolymers exhibit an essentiallysingular melting point characteristic, with a peak melting point(T_(m)), as determined by Differential Scanning Colorimetry (DSC), offrom about 60° C. to 110° C. Preferably, the homogeneous copolymer has aDSC peak T_(m) of from about 90° C. to 110° C. As used herein, thephrase “essentially single melting point” means that at least about 80%,by weight, of the material corresponds to a single T_(m) peak at atemperature within the range of from about 60° C. to 110° C., andessentially no substantial fraction of the material has a peak meltingpoint in excess of about 115° C., as determined by DSC analysis. DSCmeasurements are made on a Perkin Elmer System 7 Thermal AnalysisSystem. Melting information reported are second melting data, i.e., thesample is heated at a programmed rate of 10° C./min. to a temperaturebelow its critical range. The sample is then reheated (2nd melting) at aprogrammed rate of 10° C./min.

[0073] A homogeneous ethylene/alpha-olefin copolymer can, in general, beprepared by the copolymerization of ethylene and any one or morealpha-olefin. Preferably, the alpha-olefin is a C₃-C₂₀ a-monoolefin,more preferably, a C₁-C₁₂ a-monoolefin, still more preferably, a C₄-C₈a-monoolefin. Still more preferably, the alpha-olefin comprises at leastone member selected from the group consisting of butene-1, hexene-1, andoctene-1, i.e., 1-butene, 1-hexene, and 1-octene, respectively. Mostpreferably, the alpha-olefin comprises octene-1, and/or a blend ofhexene-1 and butene-1.

[0074] Processes for preparing homogeneous polymers are disclosed inU.S. Pat. No. 5,206,075, U.S. Pat. No. 5,241,031, and PCT InternationalApplication WO 93/03093, each of which is hereby incorporated byreference thereto, in its entirety. Further details regarding theproduction and use of one genus of homogeneous ethylene/alpha-olefincopolymers are disclosed in U.S. Pat. No. 5,206,075, to HODGSON, Jr.;U.S. Pat. No. 5,241,031, to MEHTA; PCT International Publication NumberWO 93/03093, in the name of Exxon Chemical Company; PCT InternationalPublication Number WO 90/03414, in the name of Exxon Chemical Patents,Inc., all four of which are hereby incorporated in their entireties, byreference there. Still another genus of homogeneousethylene/alpha-olefin copolymers is disclosed in U.S. Pat. No.5,272,236, to LAI, et. al., and U.S. Pat. No. 5,278,272, to LAI, et.al., both of which are hereby incorporated in their entireties, byreference thereto.

[0075] As used herein, the term “polyolefin” refers to any polymerizedolefin, which can be linear, branched, cyclic, aliphatic, aromatic,substituted, or unsubstituted. More specifically, included in the termpolyolefin are homopolymers of olefins, copolymers of olefins,copolymers of an olefin and an non-olefinic comonomer copolymerizablewith the olefin, such as vinyl monomers, modified polymers thereof, andthe like. Specific examples include polypropylene homopolymers,polyethylene homopolymers, polybutene, propylene/alpha-olefincopolymers, ethylene/alpha-olefin copolymers, butene/alpha-olefincopolymers, ethylene/vinyl acetate copolymers, ethylene/ethyl acrylatecopolymers, ethylene/butyl acrylate copolymers, ethylene/methyl acrylatecopolymers, ethylene/acrylic acid copolymers, ethylene/methacrylic acidcopolymers, modified polyolefin resins, ionomer resins,polymethylpentene, etc. The modified polyolefin resins include modifiedpolymers prepared by copolymerizing the homopolymer of the olefin orcopolymer thereof with an unsaturated carboxylic acid, e.g., maleicacid, fumaric acid or the like, or a derivative thereof such as theanhydride, ester or metal salt or the like. It could also be obtained byincorporating into the olefin homopolymer or copolymer, an unsaturatedcarboxylic acid, e.g., maleic acid, fumaric acid or the like, or aderivative thereof such as the anhydride, ester or metal salt or thelike.

[0076] As used herein, terms identifying polymers, such as polyamide,polyester, “polyurethane”, etc., are inclusive of not only polymerscomprising repeating units derived from monomers known to polymerize toform a polymer of the named type, but are also inclusive of comonomers,derivatives, etc., which can copolymerize with monomers known topolymerize to produce the named polymer. Derivatives also includeionomers of the polymer(s). For example, the term “polyamide”encompasses both polymers comprising repeating units derived frommonomers, such as caprolactam, which polymerize to form a polyamide, aswell as copolymers derived from the copolymerization of caprolactam witha comonomer which when polymerized alone does not result in theformation of a polyamide. Furthermore, terms identifying polymers arealso inclusive of “blends” of such polymers with other polymers of adifferent type.

[0077] As used herein, the phrase “anhydride functionality” refers toany form of anhydride functionality, such as the anhydride of maleicacid, fumaric acid, etc., whether blended with one or more polymers,grafted onto a polymer, or copolymerized with a polymer, and, ingeneral, is also inclusive of derivatives of such functionalities, suchas acids, esters, and metal salts derived therefrom.

[0078] As used herein, the phrase modified polymer, as well as morespecific phrases such as “modified ethylene vinyl acetate copolymer”,and “modified polyolefin” refer to such polymers having an anhydridefunctionality, as defined immediately above, grafted thereon and/orcopolymerized therewith and/or blended therewith. Preferably, suchmodified polymers have the anhydride functionality grafted on orpolymerized therewith, as opposed to merely blended therewith.

[0079] As used herein, the phrase “anhydride-modified polymer” refers toone or more of the following: (1) polymers obtained by copolymerizing ananhydride-containing monomer with a second, different monomer, and (2)anhydride grafted copolymers, and (3) a mixture of a polymer and ananhydride-containing compound.

[0080] As used herein, the phrase “ethylene alpha-olefin copolymer”, and“ethylene/alpha-olefin copolymer”, refer to such heterogeneous materialsas linear low density polyethylene (LLDPE), and very low and ultra lowdensity polyethylene (VLDPE and ULDPE); and homogeneous polymers such asmetallocene catalyzed polymers such as EXACT (TM) materials supplied byExxon, and TAFMER (TM) materials supplied by Mitsui PetrochemicalCorporation. These materials generally include copolymers of ethylenewith one or more comonomers selected from C₄ to C₁₀ alpha-olefins suchas butene-1 (i.e., 1-butene), hexene-1, octene-1, etc. in which themolecules of the copolymers comprise long chains with relatively fewside chain branches or cross-linked structures. This molecular structureis to be contrasted with conventional low or medium densitypolyethylenes which are more highly branched than their respectivecounterparts. LLDPE, as used herein, has a density usually in the rangeof from about 0.91 grams per cubic centimeter to about 0.94 grams percubic centimeter. Other ethylene/alpha-olefin copolymers, such as thelong chain branched homogeneous ethylene/alpha-olefin copolymersavailable from the Dow Chemical Company, known as AFFINITY (TM) resins,are also included as another type of ethylene alpha-olefin copolymeruseful in the present invention.

[0081] In general, the ethylene/alpha-olefin copolymer comprises acopolymer resulting from the copolymerization of from about 80 to 99weight percent ethylene and from 1 to 20 weight percent alpha-olefin.Preferably, the ethylene alpha-olefin copolymer comprises a copolymerresulting from the copolymerization of from about 85 to 95 weightpercent ethylene and from 5 to 15 weight percent alpha-olefin.

[0082] As used herein, the phrases “inner layer” and “internal layer”refer to any layer, of a multilayer film, having both of its principalsurfaces directly adhered to another layer of the film.

[0083] As used herein, the phrase “outer layer” refers to any film layerof a multilayer film having only one of its principal surfaces directlyadhered to another layer of the film.

[0084] As used herein, the phrase “inside layer” refers to the outerlayer, of a multilayer film packaging a product, which is closest to theproduct, relative to the other layers of the multilayer film.

[0085] As used herein, the phrase “outside layer” refers to the outerlayer, of a multilayer film packaging a product, which is furthest fromthe product relative to the other layers of the multilayer film.

[0086] As used herein, the phrase “directly adhered”, as applied to filmlayers, is defined as adhesion of the subject film layer to the objectfilm layer, without a tie layer, adhesive, or other layer therebetween.In contrast, as used herein, the word “between”, as applied to a filmlayer expressed as being between two other specified layers, includesboth direct adherence of the subject layer between to the two otherlayers it is between, as well as including a lack of direct adherence toeither or both of the two other layers the subject layer is between,i.e., one or more additional layers can be imposed between the subjectlayer and one or more of the layers the subject layer is between.

[0087] As used herein, the term “core”, and the phrase “core layer”, asapplied to multilayer films, refer to any internal film layer which hasa primary function other than serving as an adhesive or compatibilizerfor adhering two layers to one another. Usually, the core layer orlayers provide the multilayer film with a desired level of strength,e.g., modulus, and/or optics, and/or added abuse resistance, and/orspecific impermeability.

[0088] As used herein, the phrases “seal layer” and “sealant layer”,with respect to multilayer films, refers to an outer film layer, orlayers, involved in the sealing of the film to itself or another layer.It should also be recognized that in general, the outer 0.5 to 3 mils ofa film can be involved in the sealing of the film to itself or anotherlayer. With respect to packages having only fin-type seals, as opposedto lap seals, the phrase “sealant layer” generally refers to the insidefilm layer of a package, as well as supporting layers adjacent thissealant layer often being sealed to itself, and frequently serving as afood contact layer in the packaging of foods.

[0089] As used herein, the phrase “tie layer” refers to any internallayer having the primary purpose of adhering two layers to one another.

[0090] As used herein, the phrase “skin layer” refers to an outsidelayer of a multilayer film in packaging a product, this skin layer beingsubject to abuse.

[0091] As used herein, the phrase “bulk layer” refers to any layer of afilm which is present for the purpose of increasing theabuse-resistance, toughness, modulus, etc., of a multilayer film. Bulklayers generally comprise polymers which are inexpensive relative toother polymers in the film which provide some specific purpose unrelatedto abuse-resistance, modulus, etc.

[0092] As used herein, the term “extrusion” is used with reference tothe process of forming continuous shapes by forcing a molten plasticmaterial through a die, followed by cooling or chemical hardening.Immediately prior to extrusion through the die, the relativelyhigh-viscosity polymeric material is fed into a rotating screw ofvariable pitch, which forces it through the die.

[0093] As used herein, the term “coextrusion” refers to the process ofextruding two or more materials through a single die with two or moreorifices arranged so that the extrudates merge and weld together into alaminar structure before chilling, i.e., quenching. Coextrusion can beemployed in film blowing, free film extrusion, and extrusion coatingprocesses.

[0094] As used herein, the phrase “machine direction”, hereinabbreviated “MD”, refers to a direction “along the length” of the film,i.e., in the direction of the film as the film is formed duringextrusion and/or coating.

[0095] As used herein, the phrase “transverse direction”, hereinabbreviated “TD”, refers to a direction across the film, perpendicularto the machine or longitudinal direction.

[0096] As used herein, the phrase “free shrink” refers to the percentdimensional change in a 10 cm×10 cm specimen of film, when subjected toselected heat, as measured by ASTM D 2732, as known to those of skill inthe art.

[0097] According to the first aspect of the present invention as setforth above, if the first polyolefin comprises ethylene/unsaturatedacid, propylene/unsaturated acid, and/or butene/unsaturated acid,preferably the unsaturated acid mer is present in an amount of fromabout 4 to 30 weight percent, based on the weight of the copolymer; morepreferably, from about 7 to 20 percent; still more preferably, fromabout 8 to 15 percent; and, yet still more preferably, from about 9 to13 percent. Depending upon the meat product, if the unsaturated acid meris present in an amount less than 6 weight percent, sufficientpurge-resistance may not be achieved upon cooking the meat product inthe casing. On the other hand, if the amount of unsaturated acid mer ispresent in an amount greater than about 20 weight percent, the softeningpoint of the unsaturated acid copolymer may be too low to facilitatefilm production and/or obtain satisfactory seal strength for cook-in enduse. Thus, the optimal level of unsaturated acid mer depends on themanner in which the film is produced, and the particular end-use of thefilm, e.g., the type of meat being packaged, and the cook-in conditions.

[0098] If the first polyolefin comprises anhydride-containing polyolefincomprising an anhydride-functionality, preferably the anhydridefunctionality is present in an amount of from about 1 to 10 weightpercent, based on the weight of the anhydride-containing polyolefin;more preferably, from about 2 to 5 weight percent.

[0099] In a lap-sealed backseamed casing according the presentinvention, preferably the first polyolefin has a vicat softening pointof at least 70° C., more preferably at least 80° C., and still morepreferably at least 90° C., in order to provide a desired level of sealstrength. However, in a butt-sealed backseamed casing according to thepresent invention, in which a butt-tape film is sealed to the outersurface of the third film layer, the lower-limit of the softening pointof the first polyolefin may be less critical.

[0100] Preferably, the first polyolefin is present in the first outerlayer in an amount of from about 10 to 50 weight percent, based on theweight of the first layer; more preferably, in an amount of from about10 to 30 percent; and still more preferably, in an amount of from about15 to 25 percent.

[0101] As the third polyolefin, LLDPE is more preferred thanpropylene/ethylene copolymer because LLDPE produces a seal having less“pucker”, if the second polyolefin also comprises LLDPE and the casingis a lap-seal backseamed casing. The third polyolefin provides the firstlayer with a high melting point resin, which is advantageous for cook-inend use, where the casing is subjected to relatively high temperaturesfor a relatively long period of time. Preferably, the third polyolefinhas a melting point less than 160° C.; more preferably, less than 140°C., and still more preferably, less than 130° C. Preferably, the thirdpolyolefin has a vicat softening point of at least 80° C., morepreferably, at least 90° C., and still more preferably, at least 100° C.

[0102] In the second layer, the first polyamide preferably comprises atleast one member selected from the group consisting of polyamide 6,polyamide 66, polyamide 9, polyamide 10, polyamide 11, polyamide 12,polyamide 69, polyamide 610, polyamide 612, polyamide 6I, polyamide 6T,and copolymers thereof; more preferably, at least one member selectedfrom the group consisting of polyamide 6, polyamide 66 and polyamide6/66. Preferably, the first polyamide has a melting point of at least350° F.; more preferably, at least 370° F.; still more preferably, atleast 390° F.

[0103] Preferably, the second layer further comprises a third polyamidehaving a melting point of less than about 350° F. Preferably, the secondlayer comprises: (a) polyamide 6 in an amount of from about 40 to 90weight percent, based on the weight of the second layer; and (b)copolyamide 6/12 in an amount of from about 10 to 60 weight percent,based on the weight of the second layer, wherein the copolyamide 6/12comprises caprolactam mer in an amount of from about 30 to 70 weightpercent (more preferably, 40 to 60 weight percent). Preferably, thefirst polyamide has a melting point above 350° F., and the thirdpolyamide has a melting point below 350° F., as this combination hasbeen found to produce a combination of modulus, orientability, sealstrength, and pinhole-resistance which is preferred.

[0104] Preferably, the second polyolefin comprises at least one memberselected from the group consisting of polyethylene homopolymer,polyethylene copolymer, polypropylene homopolymer, polypropylenecopolymer, polybutene homopolymer, and polybutene copolymer. Morepreferably, the second polyolefin comprises at least one member selectedfrom the group consisting of ethylene/alpha-olefin copolymer,propylene/alpha-olefin copolymer, butene/alpha-olefin copolymer,ethylene/unsaturated ester copolymer, and ethylene/unsaturated acidcopolymer. Still more preferably, the second polyolefin comprises atleast one member selected from the group consisting of linear lowdensity polyethylene (LLDPE), propylene/ethylene copolymer, andpropylene/butene copolymer. Yet still more preferably, the secondpolyolefin comprises LLDPE. In a lap-seal backseam casing according tothe present invention, preferably the second polyolefin and the thirdpolyolefin are the same polymer.

[0105] If the fifth and sixth layers each comprise polystyrene orpolyurethane, they may be the same polystyrene and/or polyurethane, ordifferent polystyrenes and/or polyurethanes. In serving as tie layers,preferably the fifth and sixth layers each assist the adhesion of thepreferably polyolefinic first and third layers to the polyamide layer,as well as to the O₂-barrier layer, if present.

[0106] The butt-seal tape film is chosen so that it is seal-compatiblewith the sealant surface of the casing film. Preferably, the butt-sealtape film comprises polyolefin as an outer sealing layer. Morepreferably, the butt-seal tape film further comprises an O₂-barrierlayer. Still more preferably, the butt-seal tape film further comprisestwo tie layers, i.e., a tie layer between the O₂-barrier layer and eachof the two outer layers, each of which comprise polyolefin. Preferably,the butt-seal tape film is heat-shrinkable, and preferably, thebutt-seal tape film comprises an outer sealing layer comprisingpolyolefin having a melting point of from about 90° C.-150° C.; morepreferably, from about 100° C.-130° C.

[0107] The seal layer of the butt-seal tape film is an outer film layerwhich preferably comprises at least one member selected from the groupconsisting of polyethylene homopolymer, polyethylene copolymer,polypropylene homopolymer, polypropylene copolymer, polybutenehomopolymer, and polybutene copolymer; more preferably,ethylene/alpha-olefin copolymer, propylene/alpha-olefin copolymer,butene/alpha-olefin copolymer, ethylene/unsaturated ester copolymer, andethylene/unsaturated acid copolymer; still more preferably, linear lowdensity polyethylene (LLDPE), propylene/ethylene copolymer, andpropylene/butene copolymer.

[0108] In the casing film according to the third aspect of the presentinvention, all of the various polymers present in each of the filmlayers are preferably as described above according to the first aspectof the present invention, except that the first polyolefin of the firstlayer has surface energy of less than 34 dynes/cm, more preferably, lessthan 32 dynes/cm. Thus, in the third aspect of the present invention,the first polyolefin preferably comprises at least one member selectedfrom the group consisting of polyethylene homopolymer, polyethylenecopolymer, polypropylene homopolymer, polypropylene copolymer,polybutene homopolymer, and polybutene copolymer. More preferably, thefirst polyolefin comprises at least one member selected from the groupconsisting of ethylene/alpha-olefin copolymer, propylene/alpha-olefincopolymer, butene/alpha-olefin copolymer, ethylene/unsaturated acidcopolymer, and ethylene/unsaturated ester copolymer. Still morepreferably, the first polyolefin comprises at least one member selectedfrom the group consisting of linear low density polyethylene (LLDPE),propylene/ethylene copolymer, and propylene/butene copolymer. Yet stillmore preferably, the first polyolefin comprises LLDPE.

[0109] Preferably, the multilayer film has a shrink tension of at leastabout 10 psi, more preferably, from about 20-1000 psi, still morepreferably, from about 100 to 600 psi; and yet still more preferably,from about 300 to 500 psi.

[0110] A preferred backseamed casing according to the present inventioncomprises a multilayer heat shrinkable film comprising a meat-adhesionlayer comprising a polar polymer, which provides a high level of meatadhesion, especially to intermediate/high protein-containing meatproducts. Although this film can be corona treated, the film of theinvention does not require corona treatment in order to exhibit adesired level of meat adhesion with products such as turkey,good-to-intermediate quality ham, and roast beef. However, thebackseamed casing film of the present invention can be corona treated inorder to provide an enhanced level of adhesion, especially with high fatproducts. Typically, films which by themselves have a relatively lowlevel of meat-adhesion exhibit the buffing-off problem described above,at least at the backseamed edges thereof. However, the films of thepresent invention have an advantage in that respect. Because theuntreated films already have an acceptable level of meat-adhesion tointermediate-quality meat products, even when the corona treatment isbuffed-off the surface during the backseaming operation, there issufficient protein-adhesion from the polymer to prevent purge orfatting-out. Thus, the ultimate package still has an acceptable level ofadhesion. Optionally, corona treatment could also be carried out afterthe backseamed tubing is made. Here, too, if a relativelylow-meat-adhering-polymer is used as the inside casing layer and theresulting backseamed tubing is then corona treated, substantial purge(also known as cook-out and fatting-out) can occur on a strip at theedge of the backseamed tubing, where there is insufficient coronatreatment (inherent in the process used to internally corona treat).However, the corona treatment of a film surface which already has anenhanced level of meat-adhesion (as is the case in the presentinvention) reduces or eliminates the purge or cook-loss at the casinglay flat edges (which, as described above, have not been substantiallytreated). Thus, the backseamed casing of the present invention avoidsthe “buffing off problem” associated with corona treatment, while at thesame time achieving a satisfactory level of meat adhesion to variousdifferent kinds of protein-containing meat products.

[0111] As described above, the second layer of the casing film must havea thickness of at least about 5% of a total thickness of theheat-shrinkable casing film. That is, if the thickness of the secondlayer is less than about 5 percent of the total thickness of the film,the second layer may not perform adequately in preventing the film fromshrinking down against the forming shoe.

[0112] If the heat-shrinkable casing film in the backseamed casing ismade by orienting a tape which is heated over a very short time period,such as a tape heated by infrared radiation, the thickness of the secondlayer could be as high as 70%, based on the thickness of the multilayerfilm. However, if the film is heated over a relatively long time period,such as being heated in hot water, the preferred polyamides tend tocrystallize to a relatively high level before the orientation step,which produces problems during the orientation step (the rate ofcrystallization depends on the type of polyamide used). In this lattersituation, typically, the greater the thickness of the second layer, themore difficult it is to orient to obtain the resulting casing film. Thisforces a practical limit on the maximum percentage thickness of thesecond layer (especially when the most preferred polyamides are used),based on the total thickness of the multilayer casing film. Thus, ifhot-water is used as the orientation medium, the second layer of thecasing film preferably has a thickness of from about 5 to 50 percent ofthe total thickness of the casing film; more preferably, from about 5 to40 percent; still more preferably, from about 10 to 30 percent; and yetstill more preferably, from about 10 to 20 percent, based on a totalthickness of the multi-layer film.

[0113] It has been discovered that the second layer, which preferablycomprises polyamide, serves to prevent necking down on the forming shoeduring the backseaming process. Necking down typically occurs during thebackseaming process when the film is drawn so tightly around the formingshoe (as a result of the film shrinking due to the heat generatedoutwards from the seal area during the backseaming process) that itcannot be forwarded. The presence of the second layer, significantlyreduces the necking down- of the film by reducing that region of thefilm which shrinks due to the propagation of heat outward from the heatseal bar.

[0114] Preferably, the backseamed casing of the present inventioncomprises a casing film having from 3 to 20 layers; more preferably,from 4 to 12 layers; still more preferably, from 6 to 10 layers.

[0115] Preferably, the multilayer casing film used in the backseamedcasing according to the present invention can have any total thicknessdesired, so long as the film provides the desired properties for theparticular packaging operation in which the film is used. Preferably,the casing film used in the present invention has a total thickness,i.e., a combined thickness of all layers, of from about 0.5 to 10 mils(1 mil equals 0.001 inch); more preferably, from about 1 to 8 mils; andstill more preferably, from 2 to 4 mils.

[0116] It should be noted that the modulus of the casing film should behigh enough that so that the film does not stretch to an undesirabledegree during the backseaming process. Preferably, the casing film has amodulus of at least 20,000 psi; more preferably, from about 30,000 to250,000 psi; still more preferably, from about 40,000 to 150,000 psi.;yet still more preferably, from about 45,000 to 120,000; and even yetstill more preferably, from about 50,000 to 70,000 psi. It should bekept in mind that if the modulus of the casing film is too high,problems could occur after backseaming, e.g., the film could flex-crackwhen being wound up after backseaming or cause difficulty in tracking.Furthermore, too high a modulus is especially undesirable if the film isto be used as a casing which is to undergo shirring, as films of toohigh a modulus may flex-crack during shirring. On the other hand, if themodulus of the film is too low, the film tends to stretch too muchduring backseaming, thereby producing backseamed casing of low qualityin that it does not backseam acceptably, has a wavy appearance, and/orhas ruffled edges, and/or seal pucker, and/or does not track wellthrough the machine.

[0117]FIG. 1 illustrates lap-seal backseamed casing 11 according to thepresent invention. Lap-seal backseamed casing 11 comprisesheat-shrinkable casing film 12, which is sealed to itself at backseamlap-seal 13.

[0118]FIG. 2 illustrates an enlarged cross-sectional view ofheat-shrinkable casing film 12, which is especially suited to thepackaging of meat. In FIG. 2, casing film 12 comprises: first layer 14,second layer 16, third layer 18, fourth layer 20, fifth layer 22, sixthlayer 24, seventh layer 26, and eighth layer 28.

[0119] First layer 14 is an outer film layer which serves as an insidelayer of the casing film. First layer 14 has outer meat-contact surface15 for direct contact, and adhesion to, the meat being packaged incasing 11. Preferably, first layer 14 has a thickness of from about 0.1to 3 mils; more preferably, from 0.2 to 1 mil; still more preferably,from 0.3 to 0.8 mil; and yet still more preferably, about 0.5 mils.First layer 14 comprises a polar polymer which preferably has a surfaceenergy greater than 32 dynes/cm, more preferably greater than 34dynes/cm, and still more preferably greater than 36 dynes/cm.Preferably, first layer 14 comprises a first polyolefin comprising atleast one member selected from the group consisting of:

[0120] (i) ethylene/unsaturated acid copolymer, propylene/unsaturatedacid copolymer, and butene/unsaturated acid copolymer, wherein theunsaturated acid (mer) is present in an amount of at least 4 weightpercent, based on the weight of the copolymer; and

[0121] (ii) anhydride-containing polyolefin comprising ananhydride-functionality, wherein the anhydride functionality is presentin an amount of at least 1 weight percent, based on the weight of theanhydride-containing polyolefin;

[0122] More preferably, first layer 14 comprises a first polyolefincomprising at least one member selected from the group consisting of:

[0123] (i) ethylene/unsaturated acid copolymer, propylene/unsaturatedacid copolymer, and butene/unsaturated acid copolymer, wherein theunsaturated acid (mer) is present in an amount of from about 6-30%, morepreferably from about 7-20%, still more preferably from about 8-15%, andyet still more preferably, from about 9-13%, based on the weight of thecopolymer; and

[0124] (ii) anhydride-containing polyolefin comprising ananhydride-functionality, wherein the anhydride functionality is presentin an amount of from about 1 to 10 weight percent, based on the weightof the anhydride-containing polyolefin; more preferably from about 2 to5 weight percent.

[0125] If the first polyolefin comprises unsaturated acid copolymer, ifthe unsaturated acid mer is present in an amount less than 6 weightpercent, sufficient purge resistance may not be achieved. On the otherhand, if the amount of unsaturated acid (mer) in the copolymer isgreater than about 20 weight percent, the softening point of theunsaturated acid copolymer may be too low to facilitate processing intofilm and/or obtain satisfactory seal strength during cooking. Thepreferred unsaturated acid (mer) level may vary depending on the endapplication, i.e., the type of meat product to be adhered to.

[0126] In any backseamed casing according to the present invention,preferably, the inside film layer (which serves as a food-contact layer,and, in the lap seal backseamed casing according to the presentinvention also serves as a sealant layer) does not comprise a blend ofpropylene/ethylene copolymer and homogeneous ethylene/alpha-olefincopolymer having a density of less than 0.90. That is, if this blendmakes up the majority of the seal layer, the seal strength may be lessthan preferred. Furthermore, if this blend makes up the majority of theseal layer, no core layer of polyester and/or first polyamide isrequired in order to backseam the film without a detrimental degree ofnecking down on the forming shoe.

[0127] Multilayer film 12 may be used in either a lap-seal backseamedcasing or a butt-seal backseamed casing. In a lap-seal backseamed casingsuch as casing 11, preferably the first polyolefin has a vicat softeningpoint of at least 70° C., more preferably at least 80° C., in order toretain good seal strength during cook-in. However, for a butt-sealedbackseamed casing, the lower-limit of the softening point of the firstpolyolefin may be less critical, as it is both the softening point ofthe third layer of the casing film, as well as the softening point ofthe sealant layer of the butt-seal tape film, which govern sealabilityand seal strength during cooking.

[0128] Preferably, first layer 14 further comprises a third polyolefincomprising at least one member selected from the group consisting ofpolyethylene homopolymer, polyethylene copolymer, polypropylenehomopolymer, polypropylene copolymer, polybutene homopolymer, andpolybutene copolymer. More preferably, the third polyolefin comprises atleast one member selected from the group consisting ofethylene/alpha-olefin copolymer, propylene/alpha-olefin copolymer,butene/alpha-olefin copolymer, ethylene/unsaturated acid copolymer, andethylene/unsaturated ester copolymer. Even more preferably, the thirdpolyolefin comprises at least one member selected from the groupconsisting of linear low density polyethylene (LLDPE),propylene/ethylene copolymer, and propylene/butene copolymer.Preferably, the third polyolefin has a vicat softening point of at least80° C., more preferably, at least 90° C., and even more preferably atleast 100° C. Preferably, the first polyolefin is present in an amountof from about 10-50%, more preferably, in an amount of from about10-30%, and even more preferably, in an amount of from about 15-25%,based on the composition of the first outer layer.

[0129] The third polyolefin provides first layer 14 with a highersoftening point polymer to enhance the stability of the film, and sealsthereof, during cook-in. Furthermore, the dilution of the polar polymerwith a relatively non-polar polymer, i.e., the third polyolefin, doesnot significantly decrease the purge-resistance characteristics of thefirst layer of the casing film. Preferably, first layer 14 comprises ablend of 80 weight percent LLDPE and 20 weight percentethylene/unsaturated acid copolymer.

[0130] Second layer 16 is an inner film layer which is between firstlayer 14 and third layer 18. Second layer 16 provides casing film 11with the characteristic of undergoing the backseaming operation withoutnecking down on the forming shoe. Second layer 16 also helps to providea better quality casing film by making casing film 12 easier to orient,and facilitating faster backseaming speeds, and also imparting enhancedseal strength, toughness, pin-hole resistance and elastic recovery tocasing film 12. Second layer 16 preferably comprises at least one memberselected from the group consisting of polyester, and first polyamide,i.e., polymers having relatively high modulus and/or relatively highelastic recovery. More preferably, second layer 16 comprises the firstpolyamide; still more preferably, at least one member selected from thegroup consisting of polyamide 6, polyamide 66, polyamide 9, polyamide10, polyamide 11, polyamide 12, polyamide 69, polyamide 610, polyamide612, polyamide 6I, polyamide 6T, as well as copolymers prepared fromcopolymerization of any one or more of the monomers used in thepreparation of any of these polyamides; and yet still more preferably,at least one member selected from the group consisting of polyamide 6,polyamide 66 and polyamide 6/66. Preferably, the first polyamide has amelting point of at least 350° F.; more preferably, at least 370° F.;even more preferably, at least 390° F. Preferably, second layer 16 has athickness of from about 0.05 to 1 mil; preferably, from 0.1 to 0.5 mil;more preferably, from about 0.2 to 0.4 mil, and still more preferably,about 0.3 mils.

[0131] Preferably, second layer 16 further comprises a third polyamidehaving a melting point of less than about 350° F. Preferably, secondlayer 16 comprises: (a) polyamide 6 in an amount of from about 40 to 90weight percent, based on the weight of the first inner layer; and (b)copolyamide 6/12 in an amount of from about 10 to 60 weight percent,based on the weight of the first inner layer, wherein the copolyamide6/12 comprises caprolactam (mer) in an amount of from about 30 to 70weight percent, based on the weight of the copolyamide; more preferably,from about 40 to 60 weight percent.

[0132] Third layer 18 is an outer film layer which serves as an outsideabuse-resistant and heat-seal layer of casing 11. Preferably, thirdlayer 18 has a thickness of from about 0.1 to 3 mils; more preferably,from about 0.2 to 1 mil; still more preferably, from about 0.3 to 0.8mil; and, yet still more preferably, about 0.35 to 0.65 mil.

[0133] Preferably, third layer 18 comprises at least one member selectedfrom the group consisting of second polyolefin, polystyrene, secondpolyamide, polyester, polymerized ethylene/vinyl alcohol copolymer,polyvinylidene chloride, polyether, polyurethane, polycarbonate, andstarch-containing polymer; more preferably, third layer 18 comprises thesecond polyolefin; still more preferably, at least one member selectedfrom the group consisting of polyethylene homopolymer, polyethylenecopolymer, polypropylene homopolymer, polypropylene copolymer,polybutene homopolymer, and polybutene copolymer; yet still morepreferably, third layer 18 comprises at least one member selected fromthe group consisting of ethylene/alpha-olefin copolymer,propylene/alpha-olefin copolymer, butene/alpha-olefin copolymer,ethylene/unsaturated ester copolymer, and ethylene/unsaturated acidcopolymer; and yet still even more preferably, third layer 18 comprisesat least one member selected from the group consisting of linear lowdensity polyethylene (LLDPE), propylene/ethylene copolymer, andpropylene/butene copolymer.

[0134] In a lap-seal backseam casing, the second polyolefin and thethird polyolefin are preferably the same polymer.

[0135] Preferably, the second polyolefin has a vicat softening point ofat least 80° C., more preferably, at least 90° C., and even morepreferably at least 100° C. The softening point of the second polyolefinneeds to be high enough for the casing to survive cook-in.

[0136] Fourth layer 20 is an internal layer which is between first layer14 and third layer 18, and preferably comprises a polymer havingrelatively high oxygen barrier characteristics. Preferably, fourth layer20 has a thickness of from about 0.05 to 2 mils; more preferably, from0.05 to 0.5 mil; still more preferably, from 0.1 to 0.3 mil; and yetstill more preferably, from about 0.12 to 0.17 mils. In general, fourthlayer 20 comprises at least one member selected from the groupconsisting of polymerized ethylene vinyl alcohol (EVOH), polyvinylidenechloride, fourth polyamide, polyalkylene carbonate, and polyester;preferably, at least one member selected from the group consisting ofpolymerized ethylene vinyl alcohol and fourth polyamide; morepreferably, polymerized ethylene vinyl alcohol; still more preferably,polymerized ethylene vinyl alcohol having about 44 mole percentethylene.

[0137] Fifth layer 22 and sixth layer 24 are tie layers in casing film12. Fifth layer 22 is between first layer 14 and second layer 16; sixthlayer 24 is between second layer 16 and third layer 18. As a generalrule, tie layers should have a relatively high degree of compatibilitywith barrier layers, such as polymerized EVOH, or the polyamide layer,as well as non-barrier layers, such as polymerized ethylene alpha-olefincopolymer. The composition, number, and thickness of tie layers is asknown to those of skill in the art. Preferably, fifth layer 22 and sixthlayer 24 each have a thickness of from about 0.05 to 2 mils; morepreferably, from about 0.05 to 0.5 mil; still more preferably, fromabout 0.1 to 0.3 mil; and yet still more preferably, from about 0.12 to0.17 mils. Preferably, fifth layer 22 comprises at least one memberselected from the group consisting of fourth polyolefin, polystyrene andpolyurethane; more preferably, at least one member selected from thegroup consisting of modified ethylene/alpha-olefin copolymer, modifiedethylene/unsaturated ester copolymer, and modified ethylene/unsaturatedacid copolymer. Preferably, sixth layer 24 comprises at least one memberselected from the group consisting of fifth polyolefin, polystyrene andpolyurethane; more preferably, at least one member selected from thegroup consisting of modified ethylene/alpha-olefin copolymer, modifiedethylene/unsaturated ester copolymer, and modified ethylene/unsaturatedacid copolymer.

[0138] Seventh layer 26 is a core layer between first layer 14 andsecond layer 16. Seventh layer 26 provides the multilayer casing film 12film with desired abuse, shrink, and optical characteristics, andpreferably comprises a polymer having relatively low cost whileproviding these characteristics. Preferably, seventh layer 26 has athickness of from about 0.1 to 3 mils; more preferably, from 0.2 to 1.5mils; still more preferably, from 0.3 to 1 mil; and yet still morepreferably, from about 0.50 to 0.80 mils. Preferably, seventh layer 26comprises at least one member selected from the group consisting ofpolyolefin, polyamide, polyester, and polyurethane; more preferably,polyolefin; still more preferably, at least one member selected from thegroup consisting of ethylene/alpha-olefin copolymer,propylene/alpha-olefin copolymer, butene/alpha-olefin copolymer,ethylene/unsaturated ester copolymer, and ethylene/unsaturated acidcopolymer; and yet still more preferably, a blend of 80 weight percentethylene vinyl acetate copolymer (having 6 weight percent vinyl acetatemer) with 20 weight percent high density polyethylene.

[0139] Eighth layer 28 is a core layer between second layer 16 and thirdlayer 18. Eighth layer 18 also provides the multilayer film with desiredabuse, shrink, and optical characteristics, and preferably comprises apolymer having relatively low cost while providing these attributes. Ingeneral, eighth layer 18 can have a thickness of from about 0.1 to 3mils; preferably, from 0.2 to 1.5 mil; more preferably, from 0.3 to 1mil; and still more preferably, from about 0.50 to 0.80 mils. Ingeneral, eighth layer 18 comprises at least one member selected from thegroup consisting of polyolefin, polyamide, polyester, and polyurethane;preferably, polyolefin; more preferably at least one member selectedfrom the group consisting of ethylene/alpha-olefin copolymer,propylene/alpha-olefin copolymer, butene/alpha-olefin copolymer,ethylene/unsaturated ester copolymer, and ethylene/unsaturated acidcopolymer; still more preferably, a blend of 80 weight percent ethylenevinyl acetate copolymer (having 6 weight percent vinyl acetate) with 20weight percent ethylene/unsaturated acid copolymer.

[0140] Seventh layer 26 and eighth layer 28 are typically chosen incomposition and layer thickness so as to provide a relatively flat,curl-free, heat-shrinkable casing film. Preferably, seventh layer 26 andeighth layer 28 have a composition and thickness so as to provide themultilayer film with as much cross-sectional symmetry as possible.Cross-sectional symmetry provides the film with the desiredcharacteristics of low curl and low floppiness.

[0141] If “a” represents a sum of the thicknesses of the first, fifth,and seventh layers, and “b” represents a sum of the thicknesses of thesecond, sixth, and eighth layers, then preferably, a:b is from about0.5:1 to 1.5:1, more preferably 0.7:1 to 1.3:1, still more preferably,from about 0.8:1 to 1.2:1.

[0142] In casing 11, backseam seal 13 can be formed using any one ormore of a wide variety of sealing devices, as known to those of skill inthe art, such as heat sealing via hot air and/or heated bar and/or hotwire, ultrasonic sealing, radio frequency sealing, etc. However, apreferred sealing mechanism is the use of a heated seal bar whichprovides for better sealability and can provide better ultimate sealstrength, thus providing seals capable of surviving the cooking process.

[0143]FIG. 3 illustrates alternative preferred six-layer,heat-shrinkable casing film 30 suitable for use as a lap-seal casing asillustrated in FIG. 1, as well as a butt-seal casing as illustrated inFIG. 5. As with multilayer film 12 of FIG. 2, multilayer film 30 is alsoespecially suited to the packaging of meat products which are thereaftersubjected to cook-in. Casing film 30 comprises first layer 32, secondlayer 34, third layer 36, fourth layer 38, fifth layer 40, and sixthlayer 42.

[0144] First layer 32 is an outer film layer which serves as an insidecasing film layer, and accordingly is a meat-contact layer which isanalogous to first layer 14 of FIG. 2. When in the form of casing, firstlayer 32 has inside meat-contact surface 33 for direct contact with, andadhesion to, the meat within the casing. If casing film 30 is used tomake lap-seal casing 11 as illustrated in FIG. 1, first layer 32 issealed to second layer 34 at backseam lap seal 13, this seal beinglocated where a portion of outer surface 33 overlaps outside surface 35of casing film 30. First layer 32 has the same general and preferredthickness and chemical composition as first layer 14 of FIG. 2. However,first layer 32 most preferably has a thickness of 0.8 mils.

[0145] Second layer 34 is a core layer between first layer 32 and thirdlayer 36, and in general is analogous to second layer 16 of FIG. 2.Second layer 34 has the same general and preferred thickness andchemical composition as second layer 16 of FIG. 2.

[0146] Third film layer 36 is an outer film layer which serves as anoutside, abuse-resistant heat-seal layer of casing 11. Preferably, thirdlayer 36 is analogous to third layer 18 of FIG. 1. Third layer 36 hasthe same general and preferred thickness and chemical composition asthird layer 18 of FIG. 1. However, third layer 36 most preferably has athickness of about 0.8 mils.

[0147] Fourth layer 38 is an inner layer between first layer 32 andthird layer 36, and in general is analogous to fourth layer 20 of FIG.2. Fourth layer 38 has the same general and preferred thickness andchemical composition as fourth layer 20 of FIG. 2.

[0148] Fifth layer 40 is a tie layer between first layer 32 and secondlayer 34, and in general is analogous to fifth layer 22 of FIG. 2. Fifthlayer 40 has the same general and preferred thickness and chemicalcomposition as fifth layer 22 of FIG. 2.

[0149] Sixth layer 42 is a tie layer between second layer 34 and thirdlayer 36, and in general is analogous to sixth layer 24 of FIG. 2. Sixthlayer 42 has the same general and preferred thickness and chemicalcomposition as sixth layer 24 of FIG. 2.

[0150]FIG. 4 illustrates an alternative preferred three-layer,heat-shrinkable, multi-layer casing film 44 suitable for use as alap-seal casing 11 as illustrated in FIG. 1. As with multilayer film 12of FIG. 2, multi-layer film 44 is also especially suited to thepackaging of meat products which are thereafter subjected to cook-in.Casing film 44 comprises first layer 46, second layer 48, and thirdlayer 50.

[0151] First layer 46 is an outer film layer which serves as an insidecasing film layer, and is a meat-contact layer which is analogous tofirst layer 14 of FIG. 2. When in the form of a casing, first layer 46of multilayer film 44 has inside meat-contact surface 47 for directcontact with, and adhesion to, the meat within the casing. If casingfilm 44 is used to make lap-seal casing 11 as illustrated in FIG. 1,first layer 46 is sealed to third layer 50 at backseam lap seal 13, thisseal being located where a portion of inside surface 47 overlaps aportion of outside surface 51 of casing film 44. Preferably, first layer46 has the same thickness and chemical composition as first layer 14 ofFIG. 2; more preferably, first layer 46 comprises a modified polyolefinfor improved bonding to second layer 48; still more preferably, firstlayer 46 comprises anhydride-modified LLDPE as the third polyolefin.Also, more preferably, first layer 46 has a thickness of 1.0 mil.

[0152] Second layer 48 is a core layer between first layer 46 and thirdlayer 50, and in general is analogous to second layer 16 of FIG. 2.Second layer 48 has the same general and preferred thickness andchemical composition as second layer 16 of FIG. 2.

[0153] Third layer 50 is an outer abuse-resistant layer and heat-seallayer, which is analogous to third layer 18 of FIG. 2. Preferably, thirdlayer 50 has the same thickness and chemical composition as third layer18 of FIG. 2. However, third layer 50 further comprises a modifiedpolyolefin for improved bonding to second layer 48; more preferably,third layer 50 comprises, as the second polyolefin, 100 weight percentanhydride-modified LLDPE. Also, more preferably, third layer 50 has athickness of 1.0 mil.

[0154]FIG. 5 illustrates a cross-sectional view of butt-seal backseamedcasing 52, in accordance with the present invention. Butt-sealbackseamed casing 52 comprises heat-shrinkable casing film 54 havingabutting longitudinal edges 56 and 58, and butt-seal tape 60, one sideof which is sealed to outside surface 55 of casing film 54, seals 59 and61 being in regions adjacent to and along longitudinal edges 56 and 58.In this manner, a tubular casing is provided in which a product can bepackaged, especially a meat product which is thereafter subjected tocook-in while packaged in butt-seal backseamed casing 52.

[0155]FIG. 6 illustrates preferred heat-shrinkable, multilayer film 62for use as casing film 54 in butt-seal backseamed casing 52 illustratedin FIG. 5. Multilayer film 62 comprises first layer 64, second layer 66,third layer 68, fourth layer 70, fifth layer 72, and sixth layer 74.

[0156] First film layer 64 is a meat-contact and meat adhesion which isanalogous to first layer 32 of the film of FIG. 3. First film layer 64serves as an inside casing layer, and provides meat-contact surface 65for direct contact with, and adhesion to, meat packaged in the casingwhich is thereafter subjected to cook-in. Preferably, first layer 64 hasthe same thickness and chemical composition as first layer 32 of FIG. 3.

[0157] Second layer 66 is an inner film layer which serves as a casingcore layer which reduces or eliminates necking down on the forming shoeduring the backseaming operation. Second layer 66 is between first layer64 and third layer 68, and is analogous to second layer 34 of the filmof FIG. 3. Preferably, second layer 66 has the same thickness andchemical composition as second layer 34.

[0158] Third layer 68 is an outer film layer which serves as an outsidecasing abuse-resistance and heat-seal layer, and is analogous to thirdlayer 36 of the film of FIG. 3. Preferably, third layer 68 has the samethickness and chemical composition as third layer 36.

[0159] Fourth layer 70 is an inner film layer which serves as anO₂-barrier layer, is between first film layer 64 and third film layer68, and is analogous to fourth layer 38 in film 30 of FIG. 3.Preferably, fourth layer 70 has the same thickness and chemicalcomposition as fourth layer 38.

[0160] Fifth layer 72 is an inner film layer which serves as a tielayer, and is between first film layer 64 and second film layer 66, andis analogous to fifth layer 40 in film 30 of FIG. 3. Preferably, fifthlayer 72 has the same thickness and chemical composition as fifth layer40.

[0161] Sixth layer 74 is an inner film layer which serves as a tielayer, and is between second film layer 66 and third film layer 68, andis analogous to sixth layer 42 in film 30 of FIG. 3. Preferably, sixthlayer 74 has the same thickness and chemical composition as sixth layer42.

[0162]FIG. 7 illustrates preferred heat-shrinkable, multilayer film 76for use as butt-seal tape film 60 in butt-seal backseamed casing 52illustrated in FIG. 5. Multilayer film 76 comprises first layer 78,second layer 80, third layer 82, fourth layer 84, and fifth layer 86.

[0163] First layer 78 is an outer film layer which serves as a heat-seallayer, and is analogous to third layer 68 of film 62 illustrated in FIG.6. First layer 78 serves as the outer layer of butt-seal tape film 60which is sealed to outside surface 55 of casing film 54, i.e., to formseals 59 and 61 (see FIG. 5). Preferably, first layer 78 has the samethickness and chemical composition as third layer 68.

[0164] Second layer 80 is an inner film layer between first layer 78 andthird layer 82, serves as an O₂-barrier layer, and is analogous tofourth layer 38 of multilayer film 30 illustrated in FIG. 3. Preferably,second layer 80 has the same thickness and chemical composition asfourth layer 38.

[0165] Third layer 82 is an outer film layer which serves as a butt-sealtape abuse-resistance layer, and is analogous in composition to thirdlayer 68 of film 62 illustrated in FIG. 6. Preferably, third layer 82has the same thickness and chemical composition as third layer 68.

[0166] Fourth layer 84 is an inner film layer which serves as a tielayer, is between first layer 78 and second layer 80, and is analogousto fifth layer 40 of film 30 illustrated in FIG. 3. Preferably, fourthlayer 84 has the same thickness and chemical composition as fifth layer40.

[0167] Fifth layer 86 is an inner film layer which serves as a tielayer, is between second layer 80 and third layer 82, and is analogousto sixth layer 42 of film 30 illustrated in FIG. 3. Preferably, fifthlayer 86 has the same thickness and chemical composition as sixth layer42.

[0168] It should be noted that the butt-seal tape film need not have acore layer of polyamide or polyester which prevents the butt-seal tapefilm from necking down on the forming shoe. This is due to the fact thatthe butt-seal tape occupies so little of the overall structure of thebutt-sealed backseamed casing, that the shrinkage of the tape filmduring the backseaming operation has little tendency to cause neckingdown on the forming shoe.

[0169] Backseamed casings 11 and 52 (illustrated in FIGS. 1 and 5,respectively) which use films 12, 30, 44, 62, and 76 (illustrated inFIGS. 2, 3, 4, 6, and 7, respectively), are suited to many differentforms of packaging in accordance with the present invention, includingshirred casings, bags, etc.

[0170]FIG. 8 illustrates a preferred process for making casing filmand/or butt-seal tape film for in accordance with the present invention.For example, FIG. 8 illustrates a preferred process for making the filmsillustrated in FIGS. 2, 3, 4, 6, and 7. In the process illustrated inFIG. 8, solid polymer beads (not illustrated) are fed to a plurality ofextruders (for simplicity, only extruder 88 is illustrated). Insideextruders 88, the polymer beads are degassed, following which theresulting bubble-free melt is forwarded into die head 90, and extrudedthrough an annular die, resulting in tubing tape 92 which is preferablyfrom about 15 to 30 mils thick, and preferably has a lay-flat width offrom about 2 to 10 inches.

[0171] After cooling or quenching by water spray from cooling ring 94,tubing tape 92 is collapsed by pinch rolls 96, and is thereafter fedthrough irradiation vault 98 surrounded by shielding 100, where tubingtubing 92 is irradiated with high energy electrons (i.e., ionizingradiation) from iron core transformer accelerator 102. Tubing tape 92 isguided through irradiation vault 98 on rolls 104. Preferably, tubingtape 92 is irradiated to a level of from about 40-100 kGy, resulting inirradiated tubing tape 106. Irradiated tubing tape 106 is wound uponwindup roll 108 upon emergence from irradiation vault 98, formingirradiated tubing tape coil 110.

[0172] After irradiation and windup, windup roll 108 and irradiatedtubing tape coil 110 are removed and installed as unwind roll 112 andunwind tubing tape coil 114, on a second stage in the process of makingthe film as ultimately desired. Irradiated tubing 106, being unwoundfrom unwind tubing tape coil 114, is then passed over guide roll 116,after which irradiated tubing 106 is passed through hot water bath tank118 containing hot water 120. Irradiated tubing 106 is then immersed inhot water 120 (preferably having a temperature of about 185-210° F.) fora period of about 20-60, i.e., for a time period long enough to bringthe film up to the desired temperature for biaxial orientation.Thereafter, hot, irradiated tubular tape 122 is directed through niprolls 124, and bubble 126 is blown, thereby transversely stretching hot,irradiated tubular tape 122 so that an oriented film tube 128 is formed.Furthermore, while being blown, i.e., transversely stretched, nip rolls130 have a surface speed higher than the surface speed of nip rolls 124,thereby resulting in longitudinal orientation. As a result of thetransverse stretching and longitudinal drawing, oriented film tube 128is produced, this blown tubing preferably having been both stretched ina ratio of from about 1:1.5 to 1:6, and drawn in a ratio of from about1:1.5 to 1:6. More preferably, the stretching and drawing are eachperformed at a ratio of from about 1:2 to 1:4. The result is a biaxialorientation of from about 1:2.25 to 1:36, more preferably, 1:4 to 1:16.While bubble 126 is maintained between pinch rolls 124 and 130, orientedfilm tube 128 is collapsed by rollers 132, and thereafter conveyedthrough pinch rolls 130 and across guide roll 134, and then rolled ontowind-up roll 136. Idler roll 138 assures a good wind-up. The resultingmultilayer film can be used to form backseamed casings, etc., which, inturn, can be used for the packaging of meat products, in accordance witthe present invention.

[0173] The films of the examples set forth below were prepared accordingto the process described immediately above. These examples provideadditional details on the backseamed casings, their use in the packagingof a meat product, and the unexpected results obtained from the use ofthe casing film during the backseaming process, and subsequent packagingand cook-in of the meat product.

[0174] The polymer components used to fabricate multilayer casing filmand butt-seal tape film according to the present invention may alsocontain appropriate amounts of additives typically included in suchcompositions. These additives include slip agents such as talc,antioxidants, fillers, dyes, pigments, radiation stabilizers, antistaticagents, elastomers, and like additives known to those of skill in theart of packaging films.

[0175] The backseamed casings according to the present inventioncomprise casing films and butt-seal tape films which can be prepared byany means known to those of skill in the art, e.g., via coextrusionand/or extrusion coating, and/or lamination. However, preferably thefilms are produced by coextrusion.

[0176] The backseamed casing according to the present inventionpreferably comprises a casing film (and butt-seal tape film) whichcomprises a crosslinked polymer network. Although the crosslinkedpolymer network can be produced in one or more of a variety of manners,such as chemical crosslinking and/or irradiation, preferably thecrosslinked polymer network is produced by the irradiation of a tape orfilm. Either some or all of the layers of the multilayer film cancomprise crosslinked polymer networks.

[0177] In the irradiation process, the film is subjected to an energeticradiation treatment, such as high energy electron treatment, whichinduces cross-linking between molecules of the irradiated material. Theirradiation of polymeric films is disclosed in U.S. Pat. No. 4,064,296,to BORNSTEIN, et. al., which is hereby incorporated in its entirety, byreference thereto. BORNSTEIN, et. al. discloses the use of ionizingradiation for crosslinking the polymer present in the film.

[0178] Radiation dosages are referred to herein in terms of theradiation unit “RAD”, with one million RADS, also known as a megarad,being designated as “MR”, or, in terms of the radiation unit kiloGray(kGy), with 10 kiloGray representing 1 MR, as is known to those of skillin the art. A suitable radiation dosage of high energy electrons is inthe range of up to about 16-166 kGy, more preferably about 44-139 kGy,and still more preferably, 50-80 kGy. Preferably, irradiation is carriedout by an electron accelerator and the dosage level is determined bystandard dosimetry methods.

[0179] As used herein, the phrases “corona treatment” and “coronadischarge treatment” refer to subjecting the surfaces of thermoplasticmaterials, such as polyolefins, to corona discharge, i.e., theionization of a gas such as air in close proximity to a film surface.The ionization is initiated by a high voltage passed through a nearbyelectrode, causing oxidation and other changes to the film surface.

[0180] Corona treatment of polymeric materials is disclosed in U.S. Pat.No. 4,120,716, to BONET, issued Oct. 17, 1978, which is herebyincorporated in its entirety by reference thereto. BONET disclosesimproved adherence characteristics of polyethylene, by subjecting of thepolyethylene to corona treatment, in order to oxidize the surfacethereof. U.S. Pat. No. 4,879,430, to HOFFMAN, also hereby incorporatedin its entirety by reference thereto, discloses the use of coronadischarge for the treatment of plastic webs for use in meat cook-inpackaging, with the corona treatment of the inside surface of the webincreasing the adhesion of the film to the proteinaceous material.

[0181] Although corona treatment is a method of treatment of themultilayer film of the present invention, plasma treatment of the filmmay also be used.

[0182]FIG. 9 illustrates a perspective view of package 140 in accordancewith the present invention, and FIG. 10 illustrates a cross-sectionalview through section 10-10 of FIG. 9. Package 140 comprises lap-sealcasing 144 which encases meat product 146, with casing 144 being closedat both ends by clips 142, with only one clip being illustrated in FIG.9. The lap seal portion of casing 144 comprises longitudinal outercasing film edge 148 and longitudinal inner casing film edge 150, aswell as overlap region 152 which contains the backseam seal. Casing 144comprises a multilayer casing film in accordance with the backseamedcasing of the present invention. The casing film can be, for example,any one or more of preferred multilayer films 12, 30, 44, or 62, asdescribed in detail above. Furthermore, although package 140 asillustrated comprises a lap-seal casing, alternatively the package cancomprise a butt-seal casing (preferably, as illustrated in FIG. 5), inwhich latter instance the casing further comprises a butt-seal tape,preferably as described above and as illustrated in FIGS. 5 and 7. InFIGS. 9 and 10, product 146 in the package is preferably meat, morepreferably cooked meat, and preferably inside surface 154 of casing 144is adhered to the meat product during cook-in.

[0183] The packaged product can be made by a process comprising: (A)filling a backseamed casing with a meat product, whereby a filled casingis formed; (B) closing the ends of the filled casing so that the meatproduct is encased by the backseamed casing, whereby a chub is formed;and (C) cooking the meat product encased in the backseamed casing bysubjecting the chub to cook-in, so that the meat product adheres to theinside surface of the casing. The backseamed casing is a backseamedcasing according to the present invention, preferably a preferredbackseamed casing according to the present invention.

[0184] Although in general the product in the package can be any cookedmeat product, preferably the cooked meat product comprises at least onemember selected from the group consisting of poultry, ham, beef, lamb,goat, horse, fish, liver sausage, mortadella, and bologna; morepreferably, poultry, ham, beef and bologna; even more preferably, hamand roast beef.

[0185] The invention is illustrated by the following examples, which areprovided for the purpose of representation, and are not to be construedas limiting the scope of the invention. Unless stated otherwise, allpercentages, parts, etc. are by weight.

EXAMPLE 1

[0186] A 3¾ inch wide (lay flat dimension) tube, called a “tape”, wasproduced by the coextrusion process described above and illustrated inFIG. 8, wherein the tape cross-section (from inside of tube to outsideof tube) was as follows:

[0187] 3.0 mils of LLDPE#1 (80%) and Ionomer #1 (20%)/

[0188] 3.2 mils of a blend of EVA#1 (80%) and LMDPE#1 (20%)/

[0189] 1.8 mil of anhydride grafted LLDPE#2/

[0190] 1.6 mils of a blend of Nylon#1 (50%) and Nylon#2 (50%)/

[0191] 0.8 mil of EVOH/

[0192] 0.8 mils of anhydride grafted LLDPE#2

[0193] 2.7 mils of a blend of EVA#1 (80%) and LMDPE#1 (20%)/

[0194] 3.5 mils of LLDPE #3.;

[0195] wherein:

[0196] LLDPE#1 was DOWLEX® 2045.03 linear low density polyethylene,obtained from Dow Plastics, of Freeport, Tex.;

[0197] Ionomer#1 was SURLYN® 1650 zinc-based ionomer ofethylene/methacrylic acid copolymer, obtained from E. I. DuPont deNemours, of Wilmington, Del.;

[0198] LLDPE#2 was TYMOR® 1203 linear low density polyethylene having ananhydride functionality grafted thereon, obtained from MortonInternational, of Chicago, Ill.;

[0199] EVA#1 was PE 5269T (TM) ethylene vinyl acetate copolymer,obtained from Chevron Chemical Company of Houston, Tex.;

[0200] EVOH was EVAL® LC-E105A polymerized ethylene vinyl alcohol,obtained from Eval Company of America, of Lisle, Ill.;

[0201] LMDPE#1 was DOWLEX® 2037 linear medium density polyethylene,obtained from Dow Plastics, of Freeport, Tex.;

[0202] NYLON#1 was ULTRAMID® B4 polyamide 6, obtained from BASFcorporation of Parsippany, N.J.;

[0203] NYLON#2 was GRILON® CF6S polyamide 6/12, obtained fromEMS-American Grilon Inc., of Sumter, S.C.;

[0204] LLDPE#3 was DOWLEX® 2244A linear low density polyethylene,obtained from Dow Plastics of Freeport, Tex.;

[0205] All the resins were extruded between 380° F. and 500° F., and thedie was heated to approximately 420° F. The extruded tape was cooledwith water and flattened, the flattened width being 3¾ inches wide in alay-flat configuration. The tape was then passed through a scanned beamof an electronic cross-linking unit, where it received a total dosage of64 kilo Grays (kGy), which is the equivalent of 4.5 mega Rads (MR).After irradiation, the flattened tape was passed through hot water forabout a third of a minute, the hot water having a temperature of fromabout 208° F. to 210° F. The resulting heated tape was inflated into abubble and oriented into a film tubing having a lay-flat width of 9¾inches and a total thickness of 2.3 mils. The bubble was very stable andthe optics and appearance of the film were good. The film tubing wasdetermined to have 18% free shrinkage in the longitudinal direction and29% free shrinkage in the transverse direction, when immersed in hotwater for about 8 seconds, the hot water being at a temperature of 185°F., i.e., using ASTM method D2732-83.

[0206] The film tubing, made as described immediately above, was thenslit so that it was converted into film sheet. The film sheet was foldedlongitudinally around a forming shoe with opposing lengthwise film sheetedges being overlapped. Thereafter, a lap-seal backseam casing was madeby applying a heat seal (using a hot seal bar, more particularly aNishibe Model HSP-250-SA sealing machine) longitudinally over theoverlapping regions of the film sheet. During the backseaming operation,the film was positioned so that the outside layer of the film tubing(before it was slit) formed the outside layer of the backseamed casing,with the inside layer of the film tubing forming the inside layer of thebackseamed casing. The film backseamed well, i.e., without necking downaround the forming shoe to the extent that the film ruptured or theprocess was interrupted.

[0207] The resulting backseamed casing, having with a lay-flat width ofabout 4 inches, was then clipped at one end and filled with chopped hamemulsion from the open end. The casing was then closed with a secondmetal clip and the section of meat-filled casing was cut free of theremainder of the casing, forming a package which comprises the lap-sealbackseamed casing and the ham emulsion encased in the casing. Severalsuch packages were produced, and were thereafter cooked for about 4hours at from about 145° F.-170° F. in a high humidity environment. Thecooked casings were then cooled in a cooler kept at 32° F. for severalhours. The resulting chilled packages were then examined for purge andfound to have no purge between the cooked meat product and the casingfilm. Also, several samples of backseamed casing were made, eachcontaining water as the packaged medium, and a mixture of 0.1% mineraloil and 99.9% water. These casings were evaluated for seal strengthsurvivability by cooking at 180° F. for 12 hrs, and were found to haveacceptable seal strength.

[0208] The backseamed casing was also shirred. The shirred casings werefound to have acceptable seal strength, with very few or no pinholesbeing detected.

EXAMPLE 2

[0209] A 3¾ inch wide (lay flat dimension) tape is produced by thecoextrusion process described above in FIG. 8, wherein the tapecross-section (from inside to outside) is as follows:

[0210] 6.0 mils of LLDPE#3 (80%) and ION#1 (20%)/

[0211] 1.1 mil of anhydride grafted LLDPE#2/

[0212] 2.0 mils of a blend of Nylon#1 (50%) and Nylon#2 (50%)/

[0213] 1.1 mil of EVOH/

[0214] 1.1 mils of anhydride grafted LLDPE#2/

[0215] 6.0 mils of LLDPE #3,

[0216] wherein all the resins are as identified in Example 1 above. Allthe resins are extruded at a temperature of from about 380° F. to 500°F., and the die is at approximately 420° F. The extruded tape is cooledwith water and flattened, the flattened width being 3¾ inches wide, in alay-flat configuration. The tape is then passed through a scanned beamof an electronic cross-linking unit, where it receives a total dosage of64 kilo Grays (kGy), which is the equivalent of 4.5 mega Rads (MR).After irradiation, the flattened tape is passed through hot water at208° F. to 210° F. for a period of about a third of a minute,immediately after which the heated tape is inflated into a bubble, andis oriented into tubing having a lay-flat width of 9¾ inches and a totalthickness of 2.3 mils. The bubble is stable and the optics andappearance of the film are good. The resulting film has 18% freeshrinkage in the longitudinal direction and 29% free shrinkage in thetransverse direction when it is immersed in hot water at 185° F., i.e.,using ASTM method D2732-83.

[0217] The film tubing, made as described immediately above, is thenslit lengthwise, converting the film tubing into film sheet. The filmsheet is folded longitudinally around a forming shoe with longitudinallyopposing edges being overlapped, with the overlapping regions thereafterbeing joined by applying a heat seal, using a hot-seal bar,longitudinally over the overlap, to form a lap seal using a NishibeModel HSP-250-SA sealing machine. During the backseaming operation, thefilm is positioned so that the outside layer of the film tubing (beforeit is slit) corresponds with the outside layer of the backseamed casing,with the inside layer of the film tubing corresponding with the insidelayer of the backseamed casing. The film backseams well.

[0218] The resulting backseamed casing, having a lay-flat width of about4 inches, is then clipped at one end and filled with chopped hamemulsion from the open end. The tubing is then closed with a secondmetal clip and the section of meat-filled casing is cut free of theremainder of the casing, forming a package which comprises the lap-sealbackseamed casing and the ham emulsion encased in the casing. Severalpackages are so made. Each of the packages is cooked for about 4 hoursfrom 145° F.-170° F. in a high humidity environment. The cooked packagesare then cooled in a cooler kept at 32° F. for several hours. Theresulting cooked, chilled packages are examined for purge and found tohave no purge between the cooked meat product and the inside surface ofthe backseamed casing.

[0219] Several additional packages are made from the backseamed casing,each of these packages containing a product comprising 99.9% water and0.1% mineral oil. These casings are evaluated for seal strengthsurvivability by cooking at 180° F. for 12 hours, and are found to haveacceptable seal strength.

EXAMPLE 3

[0220] A 3¾ inch wide (lay flat dimension) tubular tape is producedaccording to Example 1. The tape cross-section (from inside of tube tooutside of tube) is as follows:

[0221] 6.0 mils of Terpolyolefin#1/

[0222] 1.1 mil of anhydride grafted LLDPE#2/

[0223] 2.0 mils of a blend of Nylon#1 (50%) and Nylon#2 (50%)/

[0224] 1.1 mils of EVOH/

[0225] 1.1 mils of anhydride grafted LLDPE#2/

[0226] 6.0 mils of LLDPE #3,

[0227] wherein:

[0228] Terpolyolefin#1 is LOTADER® 3210 ethylene/butyl acrylate/maleicanhydride terpolymer, comprising about 3% anhydride functionality,obtained from Elf Atochem North America, Inc., of Philadelphia, Pa., andall the other resins areas identified in Example 1 above.

[0229] All the resins are extruded between 380° F. and 500° F., and thedie is at approximately 420° F. The extruded tape is cooled with waterand flattened, the flattened width being 3¾ inches wide, in a lay-flatconfiguration. The tape is then passed through a scanned beam of anelectronic cross-linking unit, where it receives a total dosage of 64kilo Grays (kGy), which is the equivalent of 4.5 mega Rads (MR). Afterirradiation, the flattened tape is passed through hot water at 208° F.to 210° F., inflated into a bubble, and oriented into tubing having alay-flat width of 9¾ inches and a total thickness of 2.3 mils. Thebubble is stable and the optics and appearance of the resulting tubingfilm are good. The tubing film has 18% free shrinkage in thelongitudinal direction and 29% free shrinkage in the transversedirection, when immersed in hot water for 8 seconds at 185° F., i.e.,according to ASTM method D2732-83.

[0230] The tubing film is then slit into film. The film is foldedlongitudinally around a forming shoe with opposing longitudinal edgesbeing overlapped, with the overlapping regions then being joined byapplying a heat seal (using a hot-seal bar) longitudinally over theoverlap, to form a lap-seal backseamed casing, using a Nishibe ModelHSP-250-SA sealing machine. During the backseaming operation, the filmis positioned so that the layer which corresponds with the outside layerof the film tubing (before it is slit) forms the outside layer of theresulting backseamed casing, with the layer which corresponds with theinside layer of the film tubing forms the inside layer of the resultinglap-seal backseamed casing. The film backseams well, i.e., withoutnecking down on the forming shoe to the extent that the film eitherruptures or interrupts the process.

[0231] This resulting backseamed casing, having a lay-flat width ofabout 4 inches, is then clipped at one end and filled from the open endwith chopped ham emulsion. The tubing is then closed with a second metalclip, resulting in a package, with the package thereafter being cookedfor about 4 hours from 145° F.-170° F. in a high humidity environment.The packages containing cooked ham emulsion are then cooled in a coolerfor several hours, the cooler having a temperature of about 32° F. Theresulting chilled packages are then examined for purge and found to haveno purge between the product and the plastic material.

[0232] Several other backseamed casings are filled with a mixture of99.9% water and 0.1% mineral oil. These casings are evaluated for sealstrength survivability by cooking at 180° F. for 12 hrs, and are foundto have acceptable seal strength.

EXAMPLE 4

[0233] A 3¾ inch wide (lay flat dimension) annular tape, was produced bythe coextrusion process described above and illustrated in FIG. 5,wherein the tape cross-section (from inside to outside) was as follows:

[0234] 2.8 mils of EMAA#1 /

[0235] 3.3 mils of a blend of EVA#1 (80%) and HDPE#1 (20%) /

[0236] 0.9 mils of anhydride grafted LLDPE#2 /

[0237] 1.8 mils of a blend of Nylon#1 (50%) and Nylon#2 (50%) /

[0238] 1.1 mils of EVOH /

[0239] 1.6 mils of anhydride grafted LLDPE#2 /

[0240] 2.2 mils of a blend of EVA#1 (80%) and HDPE#1 (20%) /

[0241] 3.1 mils of LLDPE #3,

[0242] wherein:

[0243] EMAA#1 was NUCREL® ARX 84-2 ethylene/methacrylic acid copolymer,obtained from E. I. DuPont de Nemours, of Wilmington, Del.;

[0244] HDPE#1 is FORTIFLEX® J60-500C-147 high density polyethylene,obtained from Solvay Polymers, Inc., Deer Park, Tex.; and

[0245] all other resins are as identified in Example 1 above.

[0246] All the resins were extruded at a temperature of from about 380°F. to 500° F., and the die was heated to approximately 420° F. Theextruded tape was cooled with water and flattened, the flattened widthbeing 3¾ inches wide, in a lay-flat configuration. The tape was thenpassed through a scanned beam of an electronic cross-linking unit, whereit received a total dosage of 64 kilo Grays (kGy), which is theequivalent of 4.5 mega Rads (MR). After irradiation, the flattened tapewas passed through hot water at 208° F. to 210° F., inflated into abubble, and oriented into film tubing having a lay-flat width of 9¾inches and a total thickness of 2.3 mils. The bubble was very stable andthe optics and appearance of the film tubing were good. The resultingfilm tubing had 18% free shrinkage in the longitudinal direction and 29%free shrinkage in the transverse direction, when immersed for 8 secondsin hot water at 185° F., i.e., using ASTM method D2732-83.

[0247] The film tubing, made as described immediately above, was thenslit longitudinally, thereby converting the film tubing into film sheet.The film sheet was folded longitudinally around a forming shoe, withopposing longitudinal edges being overlapped, with the overlappingregions of the film sheet thereafter being joined by applying a heatseal (using a hot-seal bar) longitudinally over the overlap, using aNishibe Model HSP-250-SA sealing machine. During the backseamingoperation, the film was positioned so that the outside layer of the filmtubing (before it was slit) corresponds to the outside layer of theresulting backseamed casing, with the inside layer of the film tubingcorresponding to the inside layer of the backseamed casing. The filmbackseamed well and appeared to have acceptable seal strength. The filmwas also evaluated for protein adhesion and found to have satisfactorypurge resistance with an intermediate quality ham product.

EXAMPLE 5

[0248] A 5¾ inch wide (lay flat dimension) annular tape was produced bythe coextrusion process described above and illustrated in FIG. 8,wherein the tape cross-section (from inside the tube to outside thetube) was as follows:

[0249] 3.0 mils of LLDPE#3 (80%) and EAA#1 (20%) /

[0250] 3.4 mils of a blend of EVA#1 (60%), HDPE#1 (20%) and PIG#1 (20%)/

[0251] 1.2 mil of anhydride grafted LLDPE#2 /

[0252] 1.7 mils of a blend of Nylon#1 (50%) and Nylon#2 (50%)

[0253] 1.0 mils of EVOH /

[0254] 1.1 mils of anhydride grafted LLDPE#2 /

[0255] 2.7 mils of a blend of EVA#1 (60%), EAA#1 (20%) and PIG#1 (20%)/

[0256] 3.4 mils of LLDPE #3,

[0257] wherein:

[0258] EAA#1 is PRIMACOR® 1410 ethylene/acrylic acid copolymer, obtainedfrom The Dow Chemical Company, of Midland, Mich.;

[0259] PIG#1 is EPE 10214-C opaque white color concentrate, obtainedfrom Teknor Color Company, of Pawtucket, R.I.;

[0260] all other resins were as identified in Examples 1-4, above.

[0261] All the resins were extruded at a temperature of from about 380°F. to 500° F., and the die was heated to approximately 420° F. Theextruded tape was cooled with water and flattened, the flattened widthbeing 5-3/4 inches, in a lay-flat configuration. The tape was thenpassed through a scanned beam of an electronic cross-linking unit, whereit received a total dosage of 64 kilo Grays (kGy), which is theequivalent of 4.5 mega Rads (MR). After irradiation, the flattened tapewas passed through hot water for about a third of a minute, the hotwater having a temperature of from about 208° F. to 210° F. Immediatelyupon emerging from the hot water bath, the heated tape was inflated intoa bubble, and oriented into a film tubing having a lay-flat width of 15inches and a total thickness of 2.3 mils. The bubble was very stable andthe optics and appearance of the film tubing were good. The resultingfilm tubing had 18% free shrinkage in the longitudinal direction and 29%free shrinkage in the transverse direction when immersed in hot water at185° F. for 8 seconds, i.e., using ASTM method D2732-83.

[0262] The tubing, made as described immediately above, was then slitinto film, and was converted into a lap-seal backseamed casing in themanner described in Example 1, above. The film backseamed very well.

[0263] The lap-seal backseamed casing, having a lay-flat width of about4 inches, was then clipped at one end and filled with chopped hamemulsion from the open end. The casing was then closed with a secondmetal clip, and the section of meat-filled casing is cut free of theremainder of the casing, forming a package which comprises the lap-sealbackseamed casing and the ham emulsion encased in the casing. Severalpackages were produced in this manner, with the packages thereafterbeing cooked for about 4 hours at a temperature of from 145° F. to 170°F., in a high humidity environment. The resulting cooked casings werethen cooled in a cooler kept at 32° F. for several hours. The resultingchilled casings were then examined for purge and found to have no purgebetween the product and the plastic material.

[0264] Several additional packages were produced, these additionalpackages using the same backseamed casing, but encasing a productcontaining 99.9% water and 0.1% mineral oil. These casings wereevaluated for seal strength survivability by cooking at 180° F. for 12hrs, and were found to have acceptable seal strength.

[0265] The slit film was also corona-treated to a surface energy levelof 62 dynes/cm, and then immediately folded (and overlapped)longitudinally about a second forming shoe having a size so that theresulting lap-seal backseamed casing had a lay-flat width of about 5¼inches. This backseamed casing was then clipped at one end and filledwith liver sausage emulsion from the open end. The casing was thenclosed with a second metal clip, and the section of meat-filled casingwas cut free of the remainder of the casing, forming a package whichcomprised the lap-seal backseamed casing and the liver sausage emulsionencased in the casing. Several packages were produced in this manner,with the packages thereafter being cooked for about 4 hours from 145°F.-170° F. in a high humidity environment. The resulting packagescontaining cooked meat were then cooled in a cooler kept at 32° F. forseveral hours. The resulting chilled packages were then examined forpurge and found to have good purge-resistance at the casing lay-flatedges, i.e., where the edges had rubbed against the forming shoe. Thus,even though the corona treatment at the casing lay-flat edges had been‘buffed off’, there was still sufficient affinity of the untreatedmeat-contact surface of the casing (comprising ethylene/acrylic acidcopolymer) to the liver sausage to prevent fatting out at that location.

[0266] The above backseamed casing was also shirred. The shirred casingswere found to have acceptable seal strength, with very few or nopinholes being detected.

Example 6

[0267] A 5-inch tape was produced by the coextrusion process describedabove and illustrated in FIG. 8, wherein the tape cross-section (frominside of tube to outside of tube) was as follows:

[0268] 3.0 mils of LLDPE #4 /

[0269] 5.0 mils of a blend of EVA#2 (80%) and LLDPE #1 (20%) /

[0270] 1.0 mil of anhydride grafted LLDPE#2 /

[0271] 2.5 mils of Nylon#2 /

[0272] 1.1 mils of EVOH /

[0273] 1.6 mils of anhydride grafted LLDPE#2 /

[0274] 2.4 mils of a blend of EVA#2 (80%) and LLDPE#1 (20%)/

[0275] 3.0 mils of LLDPE #3, and

[0276] wherein:

[0277] LLDPE#4 was PLEXAR® PX 360 anhydride grafted linear low densitypolyethylene, obtained from Quantum Chemical Company, of Cincinnati,Ohio;

[0278] EVA#2 was ELVAX® 3128 ethylene/vinyl acetate copolymer, obtainedfrom E. I. DuPont de Nemours & Co., of Wilmington, Del.; and

[0279] and all other the resins are as identified in Examples 1-5,above.

[0280] The tape was made and oriented into 15-inch wide tubing film inthe manner described in Example 1, above. One significant differencebetween this film and the films of Examples 1-5 is that the film of thisexample has a core layer comprising only Nylon #2, i.e., nylon 6/12,rather than containing the blend of nylon 6 and nylon 6/12. The tapeoriented acceptably, though its orientability was/is significantlyinferior to that of the tapes of Examples 1-5.

[0281] The film tubing was converted into film sheet, which in turn wasconverted into lap-seal backseamed casing in the manner described inExample 1, above. The film backseamed acceptably, though not as well asthe films of Examples 1-5. Also, when evaluated for seal strength, itwas/is discovered that, while the backseamed tubing of this exampleprobably had acceptable seal strength, its seal strength was/is inferiorto that of the films of Examples 1-5.

EXAMPLE 7 (Comparative)

[0282] A 5⅛ inch, lay-flat width, annular tape was produced by thecoextrusion process described above and illustrated in FIG. 8, whereinthe tape cross-section (from inside the tube to outside the tube) was asfollows:

[0283] 3.2 mils of LLDPE #4 /

[0284] 5.2 mils of a blend of EVA#2 (65%), LLDPE #1 (20%) and PIG#1(15%) /

[0285] 0.9 mils of anhydride grafted LLDPE#2 /

[0286] 0.7 mils of a blend of Nylon#1 (50%) and Nylon#2 (50%)

[0287] 1.1 mil of EVOH /

[0288] 1.7 mils of anhydride grafted LLDPE#2 /

[0289] 1.9 mils of a blend of EVA#2 (65%), LLDPE#1 (20%) and PIG#1 (15%)/

[0290] 3.2 mils of LLDPE#3,

[0291] wherein all the resins are as identified in Examples 1-6 above.

[0292] All the resins were extruded at a temperature of from about 380°F. and 530° F., and the die was heated to approximately 420° F. Theextruded tape was cooled with water and flattened, and had a width ofabout 5⅛ inches. This tape was then passed through the scanned beam ofan electronic crosslinking unit where the tape received a total dosageof 64 kGy. After irradiation, the flattened tape was passed through hotwater for about a third of a minute, the hot water having a temperatureof from about 204° F. to 210° F. The resulting heated tape was theninflated into a bubble in a manner so that the heated tape was convertedinto a biaxially oriented film tubing. The oriented film tubing had alay-flat width of 15 inches. The multilayer film having a totalthickness of 2.3 mils, and a free shrink in the longitudinal directionof about 18 percent, and 29 percent in the transverse direction. Freeshrink was determined by immersing the film in hot water at 185° F. forabout 8 seconds, i.e., using ASTM method D2732-83.

[0293] The tubing, made as described immediately above, was then slitinto film. The film was folded longitudinally about a forming shoe withopposed edges being joined by applying a heat seal longitudinally overthe overlapping regions of the film, in an attempt to form a lap sealusing a Nishibe Model HSP-250-SA sealing machine. During the backseamingoperation, the film was positioned so that the outside layer of thetubing (before it was slit) corresponded with the outside layer of thebackseamed tubing, with the inside layer of the tubing correspondingwith the inside layer of the backseamed tubing. However, during thisbackseaming step, the film necked down a substantial degree on theforming shoe, resulting in intermittent film rupture. Thus, the film wasnot backseamable.

Example 8 (Comparative)

[0294] A 3½ inch lay-flat annular tape was produced by the coextrusionprocess described above and illustrated in FIG. 8, wherein the tapecross-section (from inside of tube to outside of tube) was as follows:

[0295] 3.2 mils of LLDPE #4 /

[0296] 4.9 mils of a blend of EVA#2 (65%), LLDPE #1 (20%) and PIG#1(15%) /

[0297] 1.0 mil of anhydride grafted LLDPE#2 /

[0298] 2.5 mils of a blend of Nylon#1 (50%) and Nylon#2 (50%) /

[0299] 1.2 mil of EVOH /

[0300] 1.6 mils of anhydride grafted LLDPE#2 /

[0301] 1.9 mils of a blend of EVA#2 (65%), LLDPE#1 (20%), and PIG#1(15%) /

[0302] 3.2 mils of LLDPE #3,

[0303] wherein all resins are as identified in Example 7 (Comparative),as set forth above.

[0304] The tape was made and oriented into 10 inch tubing film in amanner as described above in Example 7 (Comparative). The onlysubstantial difference between the film of this example and the film ofExample 7 (Comparative) is the thickness of the nylon core layer, i.e.,in this example, the nylon core layer was about 3½ times as thick as thethickness of the nylon core layer in the film of Example 7(Comparative).

[0305] The resulting film tubing was converted into film sheet and wasthereafter further converted into a backseamed casing, these conversionprocesses being carried out in the same manner as set forth in Example 7(Comparative), above. However, contrary to the film of Example 7(Comparative), this film did not undergo substantial necking down on theforming shoe, and underwent backseaming successfully.

[0306] Nevertheless, the resulting backseamed casing of this example isnot an example of the present invention because it does not havesufficient purge resistance. However, this example demonstrated that aminimum thickness of the nylon core layer is critical to thebackseamability of a heat-shrinkable film.

[0307] The backseamed casing was also shirred. The shirred casings werefound to have acceptable seal strength, with very few or no pinholesbeing detected.

Example 9 (Comparative)

[0308] A 5⅛ inch tubular tape was produced by the coextrusion processdescribed above and illustrated in FIG. 8, wherein the tapecross-section (from inside of tube to outside of tube) was as follows:

[0309] 3.0 mils of a blend of LLDPE #4 (90%) and NYLON#2 (10%) /

[0310] 5.2 mils of a blend of LLDPE #2 (80%) and EAO#1 (25%) /

[0311] 2.0 mil of anhydride grafted LLDPE#2 /

[0312] 1.1 mil of EVOH /

[0313] 1.7 mils of anhydride grafted LLDPE#2 /

[0314] 3.2 mils of a blend of LLDPE#2 (80%) and EAO#1 (20%) /

[0315] 3.0 mils of LLDPE#3,

[0316] wherein EAO#1 was EXACT 4011 (TM) homogeneousethylene/alpha-olefin copolymer, obtained from the Exxon ChemicalCompany, of Baytown, Tex.; and all other resins are as identified inExamples 1-5 and Comparatives 1-2 above.

[0317] All the resins were extruded at a temperature of from about 380°F. to 530° F., and the die was at a temperature of about 420° F. Theextruded tape was cooled with water and flattened, the flattened widthbeing 5⅛ inches. This tape was then passed through the scanned beam ofan electronic crosslinking unit where it received a total dosage of 64kGy. After irradiation, the flattened tape was passed through hot waterfor about a third of a minute, the hot water having a temperature offrom about 204° F. to 210° F. Upon emerging from the hot water, theresulting heated tape was immediately inflated into a bubble, andoriented to result in an oriented film tube having a lay-flat width of14 inches. This film had a total thickness of 2.3 mils. The tape did notorient as well as the films described in Example 1, 4, 5, 7(comparative), and 8 (comparative), due to the absence of the nylon corelayer. The film had a free shrink of about 25 percent in thelongitudinal direction, and about 29 percent in the transversedirection. Free shrink was determined by immersing the film in hot waterfor about 8 seconds, the water having a temperature of about 185° F.,i.e., using ASTM method D2732-83.

[0318] The tubing film was converted into film sheet which wasbackseamed as described in Example 1. However, during backseaming thefilm necked down severely on the forming shoe (much more severely thanin the case of Example 7 (Comparative), thereby rupturing itself anddisrupting the process. Thus, this film was not a viable backseamablefilm. Thus, not only did the absence of the nylon core layer affectorientability of the film, but the resulting film also was notbackseamable. This comparative example highlights the importance of thenylon core layer, for backseaming as well as orientability.

Example 10 (Comparative)

[0319] A 5⅛ inch tubular tape was produced by the coextrusion process asdescribed above and illustrated in FIG. 8, wherein the tapecross-section (from inside the tube to outside the tube) was as follows:

[0320] 3.0 mils of a blend of LLDPE#4 (80%) and NYLON#2 (20%) /

[0321] 6.0 mils of a blend of LLDPE#2 (80%) and EAO#1 (20%) /

[0322] 1.0 mil of anhydride grafted LLDPE#2 /

[0323] 1.6 mils of a blend of NYLON#1 (50%) and NYLON#2 (50%) /

[0324] 1.0 mil of EVOH /

[0325] 1.7 mils of anhydride grafted LLDPE#2 /

[0326] 3.0 mils of a blend of LLDPE#2 (80%) and EAO#1 (20%) /

[0327] 3.0 mils of LLDPE#3,

[0328] wherein all resins are as identified in Examples 1-9 above. Thetape was coextruded and oriented into 14 inch wide tubing film asdescribed above in Example 9 (Comparative). The only substantialdifference between this film and the film of Example 9 (Comparative) wasthe incorporation of the nylon core layer in the film of this example.The film oriented acceptably and far superior to the film of Example 9(Comparative). The tubing was then slit into film and was backseamed bya process as described in Example 1 above. The film backseamed well, andexhibited good seal strength.

[0329] However, even though the film of this example backseamedacceptably, it is not a preferred film because it exhibited insufficientprotein adhesion, i.e., insufficient purge-resistance. However, acomparison of the backseamability of this film with the backseamabilityand orientability of the film of Example 9 (Comparative), indicate thatthe presence of the nylon core layer is critical to both backseamabilityand orientability of the resulting heat-shrinkable film.

Example 11 (Comparative)

[0330] A 5-inch tubular tape was produced by the coextrusion processdescribed above and illustrated in FIG. 8, wherein the tapecross-section (from inside the tube to outside the tube) was as follows:

[0331] 3.2 mils of LLDPE #4 /

[0332] 4.6 mils of a blend of EVA#2 (80%) and LLDPE#1 (20%) /

[0333] 1.0 mil of anhydride grafted LLDPE#2 /

[0334] 1.9 mils of a blend of Nylon#1 (50%) and Nylon#2 (50%) /

[0335] 1.1 mil of EVOH /

[0336] 1.9 mils of anhydride grafted LLDPE#2 /

[0337] 3.2 mils of a blend of EVA#2 (80%) and LLDPE#1 (20%)/

[0338] 3.1 mils of LLDPE #3, and

[0339] wherein all the resins are as identified in Example 7(Comparative), above. The tape was made and oriented into 15 inchlay-flat width film tubing in the manner described above in Example 8(Comparative). The only substantial difference between this film of thisexample and the film of Example 8 (Comparative) is that the film of thisexample was pigmented. The film was converted into film sheet and wasbackseamed as described in Example 1, above. The film sheet backseamedwell.

[0340] The backseamed casing was then used to prepare a number ofpackages which contained intermediate quality ham emulsion. The hamemulsion was prepared, cooked, and chilled in the manner described inExample 1. The resulting chilled packages were found to have significantand unacceptable purge between the meat-contact surface and the cookedmeat product. Thus, this example indicates that the protein-adhesioncharacteristic of Plexar PX 360 anhydride-containing polyolefin resin,which comprises less than about ½% anhydride functionality, isinsufficient for purge resistance with intermediate or poor quality hamproducts, i.e., products which are relatively low in protein, and aretherefore more difficult for obtaining film-to-meat adhesion. The hamproduct was the same as the ham product used in Example 1.

[0341] The film sheet was also corona-treated to a surface energy levelof 62 dynes/cm, and thereafter backseamed, with the resulting backseamedcasing being used as described immediately above, i.e., to packageintermediate quality ham product. In an examination of the chilledcasings, purge was found at areas of the casing corresponding to thelay-flat edges, i.e., where the edges had rubbed against the formingshoe, thereby causing insufficient protein adhesion. The rubbing of theedges on the forming shoe presumably “buffed” the corona treated surfaceat that location. The buffing off of the corona treatment by the formingshoe resulted in too little purge resistance. Without corona treatment,the purge-resistance afforded by the anhydride-containing meat-contactresin (Plexar® PX360, which comprises less than 1% anhydridefunctionality), without corona treatment (since it had been buffed off),is insufficient to prevent fatting out. The liver sausage product usedis the same product used in the liver sausage cook-testing of Example 5.

[0342] The backseamed casing was also shirred. The shirred casings werefound to have acceptable seal strength, with very few or no pinholesbeing detected.

Example 12 (Comparative)

[0343] A 4-inch tape was produced by the coextrusion process describedabove in FIG. 8 wherein the tape cross-section (from inside of tube tooutside of tube) was as follows:

[0344] 3.0 mils of EPC#1 /

[0345] 5.0 mils of a blend of EVA#3 (70%) and EAO#2 (30%) /

[0346] 1.4 mil of anhydride grafted LLDPE#2 /

[0347] 1.2 mils of EVOH /

[0348] 1.3 mils of anhydride grafted LLDPE#2 /

[0349] 5.0 mils of EPC#1,

[0350] and wherein:

[0351] EPC#1 was ELTEX P KS409, a propylene/ethylene copolymer, obtainedfrom from Solvay Polymers, Inc., of Deer Park, Tex.

[0352] EVA#3 was PE1651CS28, 6.5% EVA copolymer, obtained from RexeneCorporation, of Dallas, Tex.

[0353] EAO#2 was TAFMER (TM) P-0480, an ethylene/propylene copolymer,obtained from Mitsui Petrochemical Industries, Ltd., of Tokyo, Japan;and

[0354] all the other resins are as identified in Example 1 above.

[0355] The tape was made and oriented into 12 inch wide tubing film in amanner as described in Example 1, above. The tape oriented acceptably,though the orientability of the tape was inferior to the orientabilityof the tape of Example 1, probably because the tape of Example 1contained a core layer comprising nylon.

[0356] The casing film, made as described immediately above, was thenslit into film sheet. The film sheet was then corona treated on aflat-sheet corona treater to achieve a surface energy level of about 48dynes/cm on the inside layer of the tubing film, i.e., the outer filmlayer which was to form the corona-treated inside layer of the casing.After corona treating, the film sheet was folded longitudinally about aforming shoe with opposing edges being overlapped as described above.The resulting overlapping region of the film was then joined by applyinga heat seal longitudinally to the overlap, to form a lap seal, using aNishibe Model HSP-250-SA sealing machine. During the backseamingoperation, the film was positioned so that the corona-treated surfaceformed the inside layer of the resulting lap-seal casing. Although thefilm did not contain a core layer comprising nylon and/or polyester, thefilm backseamed acceptably. It is believed that the presence of theouter film layers comprising propylene/ethylene copolymer assisted inpreventing the film from shrinking back so tightly against the formingshoe that the process would have been interrupted.

[0357] The backseamed casing was then used to prepare a number ofpackages which contained liver sausage. The packages were prepared,cooked, and chilled in the manner described in Example 1. While thelap-seal backseamed casing was found to have reasonable seal strength,it was not as preferred as the casing of the present invention, due toless seal strength during cook-in, and more seal pucker after cook-in,compared with the casing films of Examples 1 and 5. Furthermore, it wasfound that during cook-in fatting out occurred at regions correspondingwith the casing lay-flat edges, i.e., where the corona-treatment hadbeen buffed off by the forming shoe.

Example 13

[0358] A 5-inch tape was produced by the coextrusion process describedabove and illustrated in FIG. 8, wherein the tape cross-section (frominside of tube to outside of tube) was as follows:

[0359] 3.7 mils of a blend of EPC#2 and EAO#3 /

[0360] 2.7 mils of anhydride grafted LLDPE#2 /

[0361] 2.0 mils of Nylon#2/

[0362] 1.0 mils of EVOH /

[0363] 2.6 mils of anhydride grafted LLDPE#2 /

[0364] 4.0 mils of a blend of EPC#2 and EAO#3,

[0365] and wherein:

[0366] EPC#2 was NOBLEN (TM) W531D propylene/ethylene copolymer,obtained from Sumitomo Chemical Company, Limited, of Tokyo, Japan;

[0367] EAO#3 was TAFMER (TM) A-4085, an ethylene-butene copolymerobtained from Mitsui Petrochemical Industries, Ltd., of Tokyo, Japan;and

[0368] all the other resins are as identified in Example 1 above.

[0369] The tape was made and oriented into 14-inch wide tubing film in amanner as described in Example 1, above. The tape oriented acceptably,though the orientability of the tape was inferior to the orientabilityof the tape of Example 1, probably because the tape of Example 1contained a core layer comprising a more preferred nylon composition.

[0370] The casing film, made as described immediately above, was thenslit into film sheet and corona treated and backseamed in the mannerdescribed in Example 12, above. The film backseamed acceptably. Aftermaking chubs from the casing film packed with liver sausage andsubjecting the chubs to cook-in as described in Example 12, the lap-sealbackseamed casing was found to have reasonable seal strength, it was notas preferred as the casing of the present invention, due to less sealstrength during cook-in, and more seal pucker after cook-in, comparedwith the casing films of Examples 1 and 5. Furthermore, it was foundthat during cook-in fatting out occurred at regions corresponding withthe casing lay-flat edges, i.e., where the corona-treatment had beenbuffed off by the forming shoe.

Example 14

[0371] A 5½-inch tape was produced by the coextrusion process describedabove in FIG. 8 wherein the tape cross-section (from inside of tube tooutside of tube) was as follows:

[0372] 2.8 mils of EPC#1 /

[0373] 5.9 mils of a blend of EVA#3 (70%) and EAO#2 (30%)

[0374] 1.5 mil of anhydride grafted LLDPE#2 /

[0375] 1.2 mils of EVOH /

[0376] 3.0 mils of NYLON#2/

[0377] 0.9 mils of anhydride grafted LLDPE#2 /

[0378] 2.4 mils of a blend of EVA#3 (70%) and EAO#2 (30%) /

[0379] 2.9 mils of EPC#1,

[0380] and wherein:

[0381] all the resins are as identified in Example 1 & 7 above. The tapewas made and oriented into 16-inch wide tubing film by a process asdescribed above in Example 1. Although the tape oriented acceptably, theorientability of the tape was inferior to the orientability of the tapeof Example 1, probably because the tape of Example 1 contained a corelayer comprising a more preferred nylon composition.

[0382] The casing film, made as described immediately above, was thenslit into film sheet and corona treated and backseamed in the mannerdescribed in Example 12, above. The film backseamed acceptably. Theresulting lap-seal backseamed casing was then shirred, with the shirredcasing then being evaluated for seal strength. The results indicatedthat while the seal strength of the shirred casings was good, theshirring process resulted in a low but more than preferred rate offormation of pinholes alongside the backseam.

[0383] The results obtained from Examples 1-6, which are according tothe present invention, as well as the results obtained from Examples7-14, reveal several important and unexpected results obtained by thepresent invention.

[0384] First, it has been discovered that a core layer of nylonsubstantially reduces, or prevents, film neck-down on the forming shoeduring the backseaming process, so long as the nylon core layer has atleast a certain minimum thickness. While the amount of nylon neededprobably depends on a variety of factors, such as composition of theremainder of the film, overall physical properties, etc., it appearsthat the nylon layer needs to have a thickness of at least about 5%,based on the total thickness of the multilayer film, if necking down onthe forming shoe is to be substantially reduced or prevented.

[0385] Second, the selection of the type of nylon can have a significantimpact on the performance of the film, not just with regard tobackseamability, but also with regard to other desired characteristics,such as improved orientability, improved sealability, improved sealstrength, and improved pinhole-resistance. Whereas seal strength issimply the strength of the seal as measured by ability to withstandcook-in, sealability is the ease of sealing, i.e., incorporates asealing window temperature, seal consistency between batches, and sealreliability during cook-in. For example, a comparison of the performanceof the backseamed casings according to Example 6 versus Example 11reveals that the core layer of a blend of nylon 6 (50%) and nylon 6/12(50%), provides better tape orientability, better sealability, betterbackseamability, and better seal strength. The influence of the nyloncore layer on backseamability is unexpected in that it cannot beexplained by the modulus, free shrink, or shrink force imparted by thenylon-containing layer. Moreover, the significant influence of the nyloncore layer on seal strength is unexpected in that the nylon core layeris not serving as a sealant layer.

[0386] Third, a comparison of Examples 12-14 with themselves and withExamples 1-11 indicates several advantages of the backseamed casingaccording to the present invention. First, although the core layercomprising polyester and/or first nylon, or first nylon having a meltingpoint of at least 300° F., provides advantages in backseamability, i.e.,of prevention of necking down on the forming shoe, this advantage can insome cases (depending on the remainder of the film composition) beobtained even without the presence of such a core layer, as is apparentfrom a comparison of Example 12 (Comparative) with Example 13(Comparative). Second, a comparison of Example 13 (Comparative) withExamples 1 and 5 indicates that even if a nylon core layer is presentand the film backseams acceptably, outer layers comprisingpropylene/ethylene copolymers are associated with seal puckering, whichis aesthetically and commercially less than preferred, as well as a lessthan preferred level of seal cook-in survival. Third, a comparison ofExample 14 with Examples 1 and 5 indicates that the casings according toExamples 1 and 5 shirred without detectable pinhole formation, incontrast to the comparative casing of Example 14. Also, a comparison ofExamples 6, 13, and 14 with Examples 1 and 5, indicates that a morepreferred nylon composition can significantly enhance the orientabilityof the tape during the formation of the film tubing.

[0387] Although the present invention has been described with referenceto the preferred embodiments, it is to be understood that modificationsand variations of the invention exist without departing from theprinciples and scope of the invention, as those skilled in the art willreadily understand. Accordingly, such modifications are in accordancewith the claims set forth below.

What is claimed is:
 1. A backseamed casing comprising a heat-shrinkablecasing film comprising: (A) a first outer layer serving as an insidecasing layer, the first outer layer comprising a first polyolefincomprising at least one member selected from the group consisting of:(i) ethylene/unsaturated acid copolymer, propylene/unsaturated acidcopolymer, and butene/unsaturated acid copolymer, wherein theunsaturated acid is present in an amount of at least 4 weight percent,based on the weight of the copolymer; and (ii) anhydride-containingpolyolefin comprising an anhydride-functionality, wherein the anhydridefunctionality is present in an amount of at least 1 weight percent,based on the weight of the anhydride-containing polyolefin; (B) a secondlayer comprising at least one member selected from the group consistingof polyester, and first polyamide; and (C) a third layer serving as anoutside casing layer, the third layer comprising at least one memberselected from the group consisting of second polyolefin, polystyrene,and second polyamide; and wherein the second layer is between the firstlayer and the third layer, and the second layer has a thickness of atleast about 5% of a total thickness of the heat-shrinkable casing film.2. The backseamed casing according to claim 1 , wherein the third layercomprises the second polyolefin.
 3. The backseamed casing according toclaim 2 , wherein the second layer comprises the first polyamide.
 4. Thebackseamed casing according to claim 2 , wherein the first layer furthercomprises a third polyolefin comprising at least one member selectedfrom the group consisting of polyethylene homopolymer, polyethylenecopolymer, polypropylene homopolymer, polypropylene copolymer,polybutene homopolymer, and polybutene copolymer.
 5. The backseamedcasing according to claim 4 , wherein the second polyolefin has a vicatsoftening point of at least 90° C., and the third polyolefin has a vicatsoftening point of at least 90° C.
 6. The backseamed casing according toclaim 5 , wherein the first polyolefin comprises an ethylene/unsaturatedacid copolymer having an unsaturated acid mer present in an amount of atleast 9 percent, based on the weight of the ethylene/unsaturated acidcopolymer.
 7. The backseamed casing according to claim 5 , wherein thethird layer comprises the second polyamide.
 8. The backseamed casingaccording to claim 2 , wherein the first polyolefin comprises anethylene/unsaturated acid copolymer, the unsaturated acid is present inan amount of at least 6 weight percent, based on the weight of theethylene/unsaturated acid copolymer.
 9. The backseamed casing accordingto claim 8 , wherein the casing film further comprises a fourth layer,the fourth layer being an inner layer serving as an O₂-barrier layer,the fourth layer comprising at least one member selected from the groupconsisting of ethylene/vinyl alcohol copolymer, polyvinylidene chloridecopolymer, polyethylene carbonate copolymer and polyamide.
 10. Thebackseamed casing according to claim 9 , wherein the second layer andthe fourth layer are directly adhered.
 11. The backseamed casingaccording to claim 9 , wherein the casing film further comprises a fifthlayer and a sixth layer, wherein: the fifth layer is between the firstlayer and the second layer, and the sixth layer is between the secondlayer and the third layer; the fifth layer comprises at least one memberselected from the group consisting of fourth polyolefin, polystyrene andpolyurethane; and the sixth layer comprises at least one member selectedfrom the group consisting of fifth polyolefin, polystyrene andpolyurethane.
 12. The backseamed casing according to claim 11 , whereina ratio of: (a) a sum of the thickness of the first layer and the fifthlayer; to (b) a sum of the thickness of the third layer and the sixthlayer is from about 0.7:1 to 1.3:1.
 13. The backseamed casing accordingto claim 11 , wherein: the fifth layer is a tie layer and comprises atleast one member selected from the group consisting of modifiedethylene/alpha-olefin copolymer, modified ethylene/unsaturated estercopolymer, and modified ethylene/unsaturated acid copolymer; and thesixth layer is a tie layer and comprises at least one member selectedfrom the group consisting of modified ethylene/alpha-olefin copolymer,modified ethylene/unsaturated ester copolymer, and modifiedethylene/unsaturated acid copolymer.
 14. The backseamed casing accordingto claim 13 , wherein: the second layer has a thickness of from about 5to 20 percent, based on a total thickness of the multilayer film; andthe fourth layer has a thickness of less than about 15%, based on atotal thickness of the multilayer film.
 15. The backseamed casingaccording to claim 13 , wherein the first polyamide comprises at leastone member selected from the group consisting of polyamide 6, polyamide66, polyamide 9, polyamide 10, polyamide 11, polyamide 12, polyamide 69,polyamide 610, polyamide 612, polyamide 6I, polyamide 6T, and copolymersthereof.
 16. The backseamed casing according to claim 15 , wherein thefirst polyamide comprises at least one member selected from the groupconsisting of polyamide 6, polyamide 66 and polyamide 6/66.
 17. Thebackseamed casing according to claim 16 , wherein the casing filmfurther comprises: a seventh layer, the seventh layer being between thefirst layer and the second layer, the seventh layer comprising a sixthpolyolefin; and an eighth layer, the eighth layer being between thesecond layer and the third layer, the eighth layer comprising a seventhpolyolefin.
 18. The backseamed casing according to claim 17 , whereinthe heat-shrinkable casing film has biaxial orientation.
 19. Thebackseamed casing according to claim 17 , wherein the casing film has afree shrink, at 185° F., of at least 10% in at least one direction. 20.The backseamed casing according to claim 19 , wherein at least a portionof the casing film comprises a crosslinked polymer network.
 21. Thebackseamed casing according to claim 1 , wherein the backseam casing isa lap-seal backseam casing.
 22. The backseamed casing according to claim1 , wherein the backseam casing is a butt-seal backseam casingcomprising both the casing film and a butt-seal tape film.
 23. Thebackseamed casing according to claim 22 , wherein the butt-seal tapefilm is heat-shrinkable.
 24. A package comprising a cooked meat productwithin a backseamed casing comprising a casing film, the cooked meatproduct being adhered to a meat-contact surface of the casing film,wherein the casing film comprises: (A) a first outer layer serving as aninside casing layer and meat-contact layer, the first outer layercomprising a first polyolefin comprising at least one member selectedfrom the group consisting of: (i) ethylene/unsaturated acid copolymer,propylene/unsaturated acid copolymer, and butene/unsaturated acidcopolymer, wherein the unsaturated acid is present in an amount of atleast 4 weight percent, based on the weight of the copolymer; and (ii)anhydride-containing polyolefin comprising an anhydride-functionality,wherein the anhydride functionality is present in an amount of at least1 weight percent, based on the weight of the anhydride-containingpolyolefin; (B) a second layer comprising at least one member selectedfrom the group consisting of polyester and first polyamide; and (C) athird outer layer serving as an outside casing layer, the third layercomprising at least one member selected from the group consisting of asecond polyolefin, polystyrene and second polyamide; and wherein thesecond layer is between the first layer and the third layer, and thesecond layer has a thickness of at least about 5% of a total thicknessof the heat-shrinkable casing film.
 25. The package according to claim24 , wherein the meat product comprises at least one member selectedfrom the group consisting of poultry, ham, beef, lamb, fish, liversausage, bologna and mortadella.
 26. The package according to claim 25 ,wherein the meat-contact surface of the first layer is corona treated,and the meat product comprises at least one member selected from thegroup consisting of liver sausage, bologna and mortadella.
 27. Thepackage according to claim 24 , wherein an outside surface of the secondlayer is corona treated.
 28. A backseamed casing comprising aheat-shrinkable casing film comprising: (A) a first outer layer servingas an inside casing layer, the first outer layer comprising a firstpolyolefin, the first outer layer having a surface energy level of lessthan about 34 dynes/cm; (B) a second layer comprising a first polyamidehaving a melting point of at least 300° F.; (C) a third layer serving asan outside casing layer, the third outer layer comprising at least onemember selected from the group consisting of a second polyolefin,polystyrene and second polyamide; and wherein the second layer isbetween the first layer and the third layer, and the second layer has athickness of at least about 5% of a total thickness of theheat-shrinkable casing film.